Hi
Welcome to the board
Wingding has no square root symbol, but has a Tick symbol (like the ones you use on a checkbox) that looks a bit like the square root symbol. That's symbol 252 in Wingdings.
To check if the symbol exists in the cell use:
=ISNUMBER(SEARCH(A1,CHAR(252)))
Remark: this checks if character 252 exists, independently of the font.