"What do you mean?" in japanese
I heard it in some animes, they pronounce it "douyokoto?" but i don't know how to write it

Question

Answer

They said "どうゆうこと［do：yu：koto］dooyuukoto"（not "douyokoto"）.
言う［iu］→［ju：］yuu
I say ［iu］. But many people say ［ju：］yuu. And some people also  say ［jutta］（ゆった）＝said. But we must write いう／いった in orthography/reference format.