You must identify a wand to effectively use it.
The rules for Wands say:
Wands use the spell trigger activation method, so casting a spell from a wand is usually a standard action that doesn’t provoke attacks of opportunity. (If the spell being cast has a longer casting time than 1 action, however, it takes that long to cast the spell from a wand.) To activate a wand, a character must hold it in hand (or whatever passes for a hand, for nonhumanoid creatures) and point it in the general direction of the target or area. A wand may be used while grappling or while swallowed whole.
If we go to the rules for using Spell Trigger Magic Items, they state:
Spell trigger activation is similar to spell completion, but it’s even simpler. No gestures or spell finishing is needed, just a special knowledge of spellcasting that an appropriate character would know, and a single word that must be spoken. Spell trigger items can be used by anyone whose class can cast the corresponding spell. This is the case even for a character who can’t actually cast spells, such as a 3rd-level paladin. The user must still determine what spell is stored in the item before she can activate it. Activating a spell trigger item is a standard action and does not provoke attacks of opportunity.
Therefore, you need to know what spells are in a Wand before you can normally use it .
Of course you could always attempt to blindly activate the wand with Use Magic Device:
Some magic items are activated by special words, thoughts, or actions. You can activate such an item as if you were using the activation word, thought, or action, even when you’re not and even if you don’t know it. You do have to perform some equivalent activity in order to make the check. That is, you must speak, wave the item around, or otherwise attempt to get it to activate. You get a +2 bonus on your Use Magic Device check if you’ve activated the item in question at least once before. If you fail by 9 or less, you can’t activate the device. If you fail by 10 or more, you suffer a mishap. A mishap means that magical energy gets released but doesn’t do what you wanted it to do. The default mishaps are that the item affects the wrong target or that uncontrolled magical energy is released, dealing 2d6 points of damage to you. This mishap is in addition to the chance for a mishap that you normally risk when you cast a spell from a scroll that you could not otherwise cast yourself.
However there are some issues with this method that are not addressed by it, to name a few:
- If you don't know the spell in the wand how do you aim it? Do you select an area as a target, a person, or is it centered on yourself?
- If the spell in the wand has a casting time of greater than a standard action, do you automatically attempt to blindly activate for that period of time?
- Is it only a single DC 25 check to attempt to activate it, or is it an additional check to be able to attempt to blindly activate it in addition to the normal check to activate the item?
Thus, much of the rules for blindly activating a magic item will be subject to GM discretion and will vary significantly from table to table.