Occult Adventures details psychic magic, not “psionics,” which is notably not “magic” at all. Paizo has never printed any psionic material—the psionic material for Pathfinder is all third-party, most notably from Dreamscarred Press. As both a disclaimer and for backing up my answer, I have worked for Dreamscarred Press, specifically on their efforts to clarify the psychic–psionic confusion.
Because there was a lot of confusion—the choice to label the material from Occult Adventures “psychic,” combined with the fact that Paizo re-used some of the Open Game Content names of psionic powers for psychic spells, caused a lot of people to think they were the same. DSP saw an immediate drop in sales as people moved to the “official” form of “psionics,” and Paizo got some bad PR over it, since they had previously claimed they would not pursue psionics and this was part of what induced DSP to move from 3.5e to Pathfinder in the first place. DSP would go on to produce an entire line of products devoted to cleaning up this mess and trying to justify psionics’ existence in a game that also has psychic magic (this is what I worked on).
Tellingly, Paizo has avoided repeating this mistake: in Pathfinder 2e, this form of magic is known as “occult magic.”
Now then, history lesson out of the way, your question: does dispel magic work on psionics, or psychic/occult magic?
Yes, dispel magic works on all of the above
You can use dispel magic to undo both psychic spells and psionic powers.
Dispelling psychic spells
Psychic magic is just that, magic, and dispel magic undoes magic. No part of Occult Adventures suggests otherwise. Psychic magic uses different spellcasting components (there are no verbal or somatic components, and instead there are thought and/or emotion components), and psychic magic can do “undercasting” which other kinds of magic cannot do, but ultimately, it is still magic, psychic spells are still spells, and so on. Nothing in Occult Adventures comes out and says this, however, as nothing ever says anything about it being dispellable—that’s just the default for magic.
But we do have some evidence we can use. The medium, mesmerist, occultist, psychic, and spiritualist all get dispel magic on their spell lists, the kineticist gets a few infusions that duplicate it (but only for certain effects), and the psychic gets a class feature to spend points to use dispel magic as a supernatural ability. None of these indicate that they fail to work on the psychic magic that these classes use, which you’d think they would.
Furthermore, there are the psychic’s “phrenic amplifications,” which state
The psychic can activate a psychic amplification only while casting a spell using psychic magic, and the the amplification modifies either the spell’s effects or the process of casting it. The spell being cast is called the linked spell. [...]
Complete Countermeasure (Ex): The psychic can spend a point from her phrenic pool to increase by 2 the DCs of concentration checks or caster level checks the linked spell requires to attempt. [...] This increase also applies to checks to dispel, counterspell, or identify the linked spell.
(Occult Adventures pg. 60)
Here we see the psychic explicitly spending resources to protect their psychic spells from dispelling. There would be no reason to have this ability if they couldn’t be dispelled in the first place. It doesn’t mention dispel magic per se, but we have other references to that.
For example, we have this
Unraveling (Sp): As a standard action, you can expend 1 point of mental focus to unravel a magical effect. This functions as a targeted dispel magic spell, but you must be adjacent to the effect to unravel it. If the effect is created by psychic magic, you receive a +5 bonus on your caster level check to unravel it. [...]
(Occult Adventures pg. 51, emphasis mine)
This is a focus power available to occultists through the abjuration implement. Note that it says it uses dispel magic, and then if you target a psychic effect with that dispel, it has special benefits. This wording makes absolutely no sense if dispel magic doesn’t work on psychic magic.
Kami Medium (Archetype)
[...]
Ofuda (Su): [...] A kami medium’s spells can’t be dispelled by dispel magic or greater dispel magic, but removing or destroying the ofuda ends the duration immediately. An ofuda must be displayed prominently and can’t be hidden
(Occult Adventures pg. 72)
This is literally the only mention in all of Occult Adventures of any psychic magic that has protection from dispel magic, and as you can see, it’s a pretty niche and unusual thing.
Psychic Detective (Investigator Archetype)
[...]
Spells: A psychic detective casts psychic spells drawn from the psychic class spell list (see page 69) [...]
Psychic Meddler (Su): [...] Starting at 5th level, the psychic investigator adds half this bonus on caster level checks to dispel psychic effects.
(Occult Adventures pg. 119-120)
The only spells on the psychic spell list that the psychic investigator uses that references dispelling are dispel magic and greater dispel magic, and the psychic investigator has no other option for dispelling. Thus, dispel magic against a psychic spell is literally the only thing that a psychic investigator could use this bonus for.
So I hope all of this is very convincing that Occult Adventures absolutely has dispel magic dispelling psychic spells.
Dispelling psionic powers
Psionics is not magic, and so that requires a bit more care. However, under Dreamscarred Press’s rules, psionics is “transparent” to magic—that is, magic affects psionics just the same as it does magic, and psionics affects magic just as it does psionics. Dispel magic and dispel psionics can both dispel both magic and psionics, despite the names. This is all described in the basic rules for psionics under “Combining Psionic and Magical Effects”.
DSP does acknowledge a highly-discouraged potential variant in which magic and psionics are not transparent. This is discussed very briefly in Ultimate Psionics, and it explicitly warns the GM that if they wish to pursue a non-transparent situation, they have a lot of work to do to get that functioning correctly. Which is why it is so heavily discouraged. However, if things are not transparent, then you could not dispel a psionic power with dispel magic, and would have to use dispel psionics instead.
