This painting is clearly wonderful, as anyone can see.
Standard kanji-kana mixed spelling.
Kana spelling of 誰, common in casual writing.
A fixed phrase composed of 誰 (who) + が (subject marker) + 見て (te-form of 見る, to see) + も (even). Literally 'even if who sees', it has become a set expression meaning 'as anyone can see'.