Just my two cents:

If one is capable of distinguishing whether his opponent is professional or not, why worry about not winning at the moment?

This is a colloquial way to translate the phrase. I left out the 逢 because it is already implied. Since 何 is sort of a rhetorical question, I placed a question mark at the end.

One could also translate the 何愁 as "why bother with", instead of "why worry about." It just depends on your preference.

I don't think "何愁" is about "worrying" or "bothering" but it's a way of expressing certainty. It's like saying like saying "if A happens how can B not happen"...

Here 逢敌能辨 means "able to size up your enemy and determine his strenths and weaknesses when confronted with him", "行家手" = “行家里手”means "an old hand, an expert, a guru, a skilled master etc.", so "逢敌能辨行家手" means "if you are good at knowing your enemy, if you are an expert in this regard, you would be a real master, a real expert." or we can put it another way, if you are an expert, you must know how to know your enemy when confronted with him. 何愁=how would it be necessary to worry, 不此时=not at this time, not on the spot, so 何愁胜利不此时 means "why do you worry that you cannot win now, on the spot, etc." So the whole sentence can be paraphrased in another way: if you are an old hand at weighing your enemy's strengths and weaknesses, how can it be that you need to worry about your victory right away?