kibitzes

Kibitzes is the third-person singular form of kibitz, meaning to watch others engaged in an activity—especially a card game—while offering unwanted advice or commentary.

The word comes from Yiddish and carries connotations of meddlesome interference rather than helpful observation.

She kibitzes during every poker night, telling everyone how they should have played their hands.

Someone who habitually does this is called a kibitzer.