Normally a creature is aware when they are under some kind of effect, but not necessarily what the effect is.
The game I am playing has allowed the Path of War rules and is also allowing some of the beta-testing material. Radiant Dawn is a new discipline in the beta-test, and it includes a strike called disrupt essence with the following description:
A powerful blow that disrupts one's essence, inhibiting the use of abilities. Make an attack. If it hits, the target must make a Will save (DC 10 + ½ your initiation level + your initiation modifier) or have a single Extraordinary (Ex) or supernatural (Su) ability that requires an action to activate, special sense, or special movement type of your choice disabled for rounds equal to your initiation modifier. You must be aware of the ability in order to disable it (Such as a successful knowledge check, or having seen it in action).
A paladin's smite evil and lay on hands abilities are Su which means that it can be affected by this strike. Assuming the paladin fails the save, they know they have been affected by something, but would they know which ability is locked away until they try to use it? Also, would trying to use the ability take up the action that it normally would and count against uses?