What is your context? In general, 'can only' is correct English. 'only can' sounds Chinglish to me. There may be some specific contexts where it makes sense, but mainly in historical sentence orders, so it generally it is not used. Can you give some examples of where it is used, and we can see whether they are correct or not?

I can't think of a sentence where 'only can' makes sense by itself. If there's a word between 'only' and 'can', then it might make sense. For example... Jeff: "Can Jim speak Spanish?" Bill: "No, Maria is the ONLY person who CAN speak Spanish. Jim CAN ONLY speak English."

I agree with Gary that we probably need to see the actual sentence, but I'd say that "can only" and "only can" mean the same thing. "Can only" is more often used. "Only can" is either a bit old-fashioned or used by someone who's English is not very good yet. Hope that helps!