I was recently invited to a party by a Facebook friend. I asked him where the party was happening, and he said he couldn't remember the address. While texting someone else about the experience, I wrote:
My friend just invited me to a party that he doesn't even know where is.
The italicized phrase is intended to be synonymous with "that he doesn't even know the location of", but I thought that alternative might sound stilted and overly formal. Would this phrase be grammatically correct?