Answer by Waylander for Reimer-Tiemann reaction on indole

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

1. 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.