Based on how I understand it.
Both radicals are exponents. I prefer to get the decimal value of each square root.
√2 = 1.414
√8 = 2.828
PEMDAS - Parenthesis, Exponents, Multiply, Divide, Add, Subtract
This is the order of operation. We need to solve first the numbers inside the parenthesis. I'll just use the decimal value.
(2^√2) ⇒ 2¹.⁴¹⁴ = 2.665
2.665^√8 ⇒ 2.665².⁸²⁸ = 15.990
(2^√2)^√8 = 15.99