Can't get bike valve caps off
Turn anti-clockwise as seen from above and use more force. You should be able to get them off by hand.

If you do destroy the caps, go to a bike store and buy replacements. Ask for 'Schrader' type caps. 

Can we assume you are borrowing a bike and need to inflate the tire? The statement 'the bike isn't mine and the owner doesn't know' is slightly troubling. If you have trouble with a borrowed bike take it back to the owner. (deleted as based on misunderstanding.)

Brand and model of bike does not matter, tube valves are either 'Schrader' (same as on car tires) or narrower 'Presta' types.