Your formatting, lacking grouping symbols, is ambiguous. For example, it could mean "sqrt[2^(3b)^(4*sqrt[8]ab)^2]", which typesets as:√2^3b ^4√8ab^2
You've "tried several times" to do what? What were the instructions? What are you supposed to be doing with this expression?I've tried several times....
√2^3b^4 √8ab^2