Q: can janaza salah be performed in musjid?
A: Janazah salah should be performed outside the musjid. If this is impossible, then it should be performed in the courtyard area or a place that is not viewed as part of the Musjid.
Performing janazah salah in the musjid reduces reward, more so when other options do exist. Performing janazah salah in the musjid would constitute makroohi tahrime (great disliked.)
(see Abu Dawood, Fatwa Qadhi khan, etc)
Allah Certainly Knows Best.