There are two possible options
Option 1 -
B says A is a knave, and C says B is lying
If C is telling the truth, that means C is a knight as knights always tell the truth. And if B is lying that means he is a knave. Also if B is lying and he says A is a knave, that means A is the opposite of...
You could ask him which way the other guy will tell you to go.
If you ask the guy who tells the truth, he will tell you the way the liar would tell you, so you would have to go the other way.
If you ask the guy who lies, he will tell you the opposite to which way the truth-teller would tell...