Answer
The lewis structure is like water with an additional H, bonded to a pair of free valence electrons. Since the overall charge of the molecule is 1+, don't forget to add brackets and a '+' sign on the top right to indicate the charge.
Work Step by Step
Unlike $H_{2}O$, notice that $H_{3}O^{+}$ has a positive charge to it, which means there is an $H^{+}$ (hydrogen) ion, which bonded to $H_{2}O$. Therefore, the lewis structure is just $H_{2}O$ with an additional H. And don't forget the brackets and the charge.
