So I've got $1 that says it's the K3 relay. I would check the simplest thing first, and that's continuity between the broiler relay and the bake element socket, breaker OFF of course. It should be very low, if your meter beeps it should be nice and clear. Since the bake element works, the schematic tells us that there is power to the K3 relay, and also to the other side of the bake element, which is not switched. Your power measurements of about 120v on that unswitched side suggest strongly that that side is OK. That you don't get power on the switched side says there's no power on the switched side of the bake element.
Where does that leave you? Somewhere power is interrupted between the switched terminal at the bake element, and the power side of the K3 relay....or the K5 relay isn't being switched. Of all of that, I'm betting on the K3 relay because it's the most complicated. They have them wired that way so that it's mechanically impossible for both the broiler and bake element to be on at the same time. K3 won't let them both connect at once. If the broiler cycles OK, but there's never any power getting to K5, then there's something wrong with the normally closed side of K3...either lots of carbon build up between the contacts, or the contacts are burned up enough that they don't touch. With the breaker off, you should be able to tell if the contacts are open or not. Normally, I'd suggest just replacing the relay, but believe those are obsolete parts.
https://www.mouser.com/datasheet/2/418/4/NG_DS_1308242_T90_0214_T90-116266.pdf
I don't think the exact relay is listed, but it would be a form 'C' in the datasheet, as a SPDT (single pole, double throw) relay. They call that configuration a 'CO'. Close/open I guess.