Sure, you could easily use a "normal" PC with enough RAM and speed. It will require only a modest disk, actually a 100GB is enough so that is small to today's standards. SSD would be good candidate. RAM needs to be at least 16GB.

Besides RAM network bandwidth will be the biggest issue. Unless you're fed with fiber (or high end cable modem?) you may have problems.

It's var more practical to rent a VPS, but if you're serious rent a dedicated server.

sorry I don't understan
I wander spec(cpu, main bord, storage,,,,,,etc)

It's good to see people interested in running a witness.

Welcome, Kasreder :)
I will let someone more knowledgeable answer your question :)

Is it possible to use a normal PC? Do I have to use a server PC?
Thank you for your quotation.