Listen and understand Sukhmani Sahib ji he is nirgun and sargun, he himself is everyone and causes all to happen to his comand, if u look at it from a worldly perspective you will be riddled with doubts , if you look at it from a Gursikhs point you and listen a believe in SGGS ji you would never ask such question or have and doubts.
Rember Waheguru ji is the creator he can do anything he wills and he has not limits or end.
He is not like us human being yet he is everyone of us.