A mesial/distal projection of cone adjustment during working length radiograph is indicated  for which tooth?
When two superimposed canals are present (for example buccal and palatal canals of maxillary premolar, mesial canals of mandibular molar) one should take following steps:

Take two individual radiographs with instrument placed in each canal.
Take radiograph at different angulations, usually 20° to 40° at horizontal angulation.
Insert two different instruments, e.g. K file in one canal, H file/reamer in other canal and take radiograph at different angulations.
Apply SLOB rule; expose the tooth from both mesial or distal horizontal angle, canal which moves to same direction, is lingual where as canal which moves to opposite direction is buccal.

Textbook of Endodontics Nisha GARG 3rd ED
Maxillary anterior teeth
Maxillary molars with a mesiolingual canal
Mandibular incisors
None of the above