What episode of dgray man does lavi and Allen fight?

Lavi and Allen don't fight in the anime or manga of D.Gray-man. They are close friends and comrades, and their relationship is characterized by their mutual respect and understanding. While they may disagree on certain things or have differing opinions, they never engage in any physical combat.

It's possible you're thinking of a different anime or manga where two characters with similar names or appearances might have fought.