Notation "5% solution"
Generally speaking, percentage aqueous solutions like that are either weight for weight or weight for volume. Either way, in this example, you are comparing how many osmoles there for the same weight of urea ($CO(NH_2)_2$) and glucose ($C_6H_{12}O_6$).

Mole fraction as expressed in a percentage does exist though I have not seen that notation much myself and is usually designated n/n%

From the wording your question I'm guessing that it's a physiology or biochemistry question, in which case they're almost certainly referring to the 5% aqueous solution of glucose as the common IV hydration fluid 5% Dextrose Solution, which is w/w.

Otherwise, it's hard to guess as it's ambiguous!