English Translation
What did he say?
he sentence “그가 뭐라고 했지?” (geuga mworago haetji?) literally means “What did he [or she] [verb implied]?” or “What was said?”
The verb “to say” can be added to the sentence to make it more explicit. So, the complete sentence with the verb included would be “그가 뭐라고 말했지?” (geuga mworago malhaetji?) which means “What did he [or she] say?” or “What was said?”