...to make sure... uses _that_ Examples: Make sure that the door is locked! Make sure that you call your mother. ...if / whether ... See whether the door is locked, please. See if you can guess what I'm thinking. I'll find out whether you called or mother or not. By the way, it's unusual to say "pays attention" -- it's more usual to say "is paying attention." And "speaking" is not correct; "saying" is needed here. Here's your sentence with choices for some of the phrases: {informal / typical / more formal}. When two people are {talking / having a conversation / in conversation}, the speaker will {look at the listener now and then / occasionally look at the listener, only look at the listener from time to time} [no comma] in order to {see if / check whether / make sure that} the listener is {paying attention. / paying attention to what is being said. / paying attention to what he or she is saying.}