when does elena get her memories of damon back

Elena gets her memories of Damon back in The Vampire Diaries when the vampirism cure restores them, after the memory-erasing storyline in Season 6. The search results point to coverage of that arc and specifically note that the cure brings her memories back.

What happens

Elena had her memories of Damon altered/erased, which is why she initially sees him very differently. Later, the storyline resolves through the cure rather than through her simply “remembering” on her own.

In context

This is part of the Season 6 Delena plot, with recap coverage highlighting Elena trying to recover what was taken from her. So the short answer is: she gets them back when the cure restores her original vampire state and its linked memories.

TL;DR

Elena gets her memories of Damon back through the cure-related plotline in Season 6, not in a random one-off scene.