Reimer-Tiemann reaction on indole 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).
The paper by Order and Lindwall [1] agrees with you that the R-T reaction gives indole-3-carboxaldehyde.


  Since its isolation in 1903 by Hopkins and Cole (1), 3-indole aldehyde has been investigated very little. It was first prepared by Ellinger (2) from indole through the use of the Reimer-Tiemann reaction. This method was improved on later by Boyd and Robson (3).


References


Order, R. B. V.; Lindwall, H. G. 3-Indole Aldehyde and Certain of Its Condensation Products. J. Org. Chem. 1945, 10 (2), 128–133. DOI: 10.1021/jo01178a006.