"Laquelle veux-tu ?"
Translation:Which one do you want?
It does not accept lequel and has no place to report that it should be accepted.
This is the feminine singular form. It needs to agree in number and gender with the object (s) it replaces. Lequel, laquelle, lesquels, lesquelles. https://www.thoughtco.com/french-pronoun-lequel-1368874
What in this sentence suggest that it is feminine? Even in the link provided by leo67981, "Lequel veux-tu" is an accepted translation.
What is the difference between Laquelle and Quelle? Can they replace each other?