My WAG would be Laos.
My guess would be Cambodia, Laos, or one of the northern Vietnam hill tribes.
I think it is Laotian. Definitely not Cambodian. Could be a Vietnamese hilltribe, because many are ethnic Thais. The only thing that makes me think it is not Thai is the transliteration spelling, as Thai and Lao names are often pronounced the same but with different transliterations. Skoulphong is pronounced “Sa-GOON- pohng” or maybe even “Sa GOONA-pohng.” A Thai would not normally include the first O. But it could be Thai. Cambodian is right out though.
FWIW, there is an Ancestry.com entry of someone with that last name being born in Laos. The house seems to be right about this one.