The One Where Eddie Moves In - S2-E17
Continuity mistake: In the previous episode, Joey tells Chandler that the bathroom in his new apartment has mirrors on both sides of the toilet. But in this episode, when we see the toilet from the side while Joey gives the gang a tour, it is clear that the wall is devoid of mirrors.
Answer: The painting doesn't have a name, and if it does it is never mentioned in this episode.