Help me with a competitors Backlinks

Hey Guys, I am new her and have a niche project to do. This is my project page: https://sugarbae.de/
I have a competitor named https://sugardad.eu/ and I know that he bought backlinks. It becomes very obvious while checking his backlink proflie on SEMrush. I would like to know where he bought the and how. How can I find out?
Thanks a lot

Very hard to find, where he bought the links but you can check the quality of the backlinks using the tools such MOZ & Ahref