Ask one of them: what would the other dude say is the correct path?
Then take the path which is not the answer.
**Although there seems to be nothing in your question suggesting that there is correct path or something.. infact, what is the reason you have to ask the guards a question in the first place? :/
im assuming u want to n which one is the liar because u would ask the same question to both of them that u know the naswer to. and if u pass by "2" paths guared by "2" men it doesnt matter what u ask them because ur just passing by