Sentence Structure: What is it or What it is? Confusing English

In this video, Alisha answers 5 questions. - Hi, Alisha. I'm a university student in the United States. I teach English to elderly students as a part-time job. one of them asked me what 'fire with fire means?' I guess the man heard the phrase through a movie. Could you tell me the meaning? - What is the difference between "I don't know what is that" and "I don't know what that is"? - Can you give an explanation about the word "roughly"? Thank you so much. - My question is about when I visit restaurants and I don't want ice in my drink, for example. How do I say it? No ice or without ice? - Is there a difference between "to lend" and "to borrow"?