You can interrogate an enemy by grabbing them RB and then whilst holding them dominate B and interrogate A. Note captains and warchiefs may not be initially be grabbable and needs to be weakened first.
The benefits of interrogation depends on the type of enemy you are questioning:
- Normal uruk: Can give the name and appearance of an unknown captain (shown as black silhouette in the army screen)
- Worm (normal uruk with green icon on their head): Can give you the above information and the traits of the captain i.e. their strengths and weaknesses.
- Captains and warchiefs: may also be interrogated and will give the same information as worm. But often needs to be weakened first before you may grab them.
Note: If there are no more unknown information regarding captains or warchiefs, the interrogate option will be replaced by kill.
It is generally useful to know the strengths and weaknesses of a captain or warchief before engaging them in combat so that you may abuse their weaknesses and look out for their strengths.