The word "its" refers to the earth. Yahweh uses more questions to emphasize that Job could never understand how great God is. (See: [[rc://en/ta/man/translate/figs-rquestion]])
This can be stated in active form. This can be translated as a statement. Alternate translation: "On what did I set its foundations?" or "Tell me on what its foundations were laid." (See: [[rc://en/ta/man/translate/figs-rquestion]] and [[rc://en/ta/man/translate/figs-activepassive]])