The Soulknife’s soulknife comes from their Psychic Blades subclass feature, which states:
“Also at 3rd level, you can manifest your psionic power as shimmering blades of psychic energy. Whenever you take the Attack action, you can manifest a psychic blade from your free hand and make the attack with that blade. This magic blade is a simple melee weapon with the finesse and thrown properties.”
So would a soulknife disappear in an antimagic field, or would it merely be a suppressed magic weapon?
If it's the later, would you be able to manifest it in an antimagic field given that it uses psionic energy to manifest even though it’s a magic weapon?
Would the other Soulknife class features that use the soulknife but aren’t described as magical still function, even if the soulknife is now a suppressed magic weapon?
Also for the parameters of the question assume that this unofficial tweet is correct: https://twitter.com/JeremyECrawford/status/1252282928576335875:
The antimagic field spell in D&D affects spells, magic items, and other effects that are expressly magical. The spell doesn't care about the source of those things (arcane, divine, psionic, or something else).
So some psionic effects would be affected and some wouldn't.