According to me net reaction should be at $\ce{C3}$ when Reimer-Tiemann reaction is done on indole (see image), since in the resonance structure, negative charge is on this carbon.
But, the answer given is on $\ce{C2}$, and the solution given is
In pyrolle, the most electrophilic site is $\ce{C2}$. Think in a similar way.
But, I can't either find fallacy in my reasoning, not do I convince with the solution.
TL;DR Where will dichlorocarbene attack on indole (am not interested in ring expansion).