Do i see a dermatologist or podiatrist regarding my toenail fungus and the black, purplish, and slightly reddish spot that's also under my toenail?

Either: As a podiatrist we treat these all day. We take a small portion of nail to verify it is fungus then give you treatment options. Dermatologists are certainly qualified so its what you are most comfortable with.

Definitely DPM: Podiatrist are the specialists when it comes to toenail fungus. We see it everyday. Just as seinfeld said to elaine in the famous podiatrist episode says, "he's into fungus!" we will have every option available to you.