I have seen both "someoneで(は)わからない" as well as "someoneに(は)わからない"
How are the nuances changed? How do they differ? Another example would be "私にわかることは....、私でわかることは...." What is the difference?
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で is basically a condition marker, which may serve as a hint. Sometimes (人)では has an implication like "if/since it's him/her/me", "if you ask him/her/me", "on one's side" etc.
私には分かりません and 私では分かりません are usually interchangeable, but the former is more simple and sounds like the problem is too difficult (to the speaker or to anyone). The latter sometimes sounds like "You're asking a wrong person".
彼には英語が話せる is a simple and natural sentence ("He can speak English"), but 彼では英語が話せる is odd. 彼には英語が話せない is simple and natural, but 彼では英語が話せない means something nuanced like "if (you ask it to) him, (he) can't speak English (so it won't work)".