Well, in the strict sense, it won't give you any skills. Though it's certainly a great avenue for developing skills. What those skills are, really depends on where you want to focus - modding a huge area.
The most obvious stuff would be basic electronics, soldering, and general hand fabrication. Depending on what side of modding you want to focus on, it can be great for learning about coding, reverse engineering, painting, 3d printing, PCB etching, and a plethora of other stuff. It can even be solid for bettering communication skills and such, since a lot of modding projects rely on collaboration and such.
Ultimately, it's about like any hobby - you can learn a lot if you apply yourself, and some of that knowledge may even be useful beyond the hobby - I, for one, have a job working with robots and flax, and I wouldn't have it if I didn't have a solid understanding of electronics, thanks to hanging out here for years.