Does 식탁 imply kitchen table or is it any table?
식탁 is table for eating. 상 is the word for any table in general. (And also 책상 means desk or table for studying.)
Any table for eating
Is it possible to leave out the "위에" and just put the "에" on the end of "식탁"? Or would that mean something closer to "... in the table."?
I said 식탁 위에 김밥이 있습니다 and was marked wrong. I reported it
시탁 could be any table, not just the kitchen table.
식 has a meaning related to food, so that's not correct. 탁자 is the general word for table.
After learning both the formal and polite forms of verbs, both verb endings should be accepted in all answers unless there is a specific context. In this sentence, there isn't a difference contextually between 있어요 and 있습니다.