For sure you can inspect motherboard visualy for parts defects, such as capacitors leaking, MosFETs and other power parts exploding or cracking, melting parts, bad pins in power connector sockets,... also you can replace the broken parts with complete new or with good parts removed from some other motherboards. For scope usage and other signal logic instruments, you need additional knowledge, you need to know when and what signal you should see on what point on motherboard. For good professional repairmans this is not problem, because they pass good training for that or have many years of expirience, even they can have special service informations about board.
In any case you can take some old PC and try something. But keep in mind that you can lose lots of time on this. Lots of things are solved based on expirience, even without scopes and other equipment.