Here’s how to find it on iPad… search for an artist and tap the entry for their artist page; tap the “About” link; scroll down on the “About” side of the page to find Similar Artists. Tap any of the Similar Artists and the app stops responding only to crash several seconds later.
I can’t seem to find the same thing on the iPhone today, though I’d swear it was there yesterday. I can’t even get the “About” info for the artist on the iPhone today.
I just tried the same thing in iTunes to see what would happen. In iTunes 12.2 (on OS X 10.10.4) the "About" section is titled "Biography." Below Biography are areas for "Similar Artists" and "Influencers." Both areas have clickable links to the artists that are listed; although you wouldn't know it from the UI. Hover over the area and the pointer does not turn into a hand, nor do the names get underlined as happens elsewhere in iTunes for clickable areas. The more I use this, the more it looks like the whole thing was rushed and unfinished.