While someone's ears pops with pressure, can he/she hear other sound at the same time?
Yes, of course they can. What happens when your ears feel 'full' like on an aeroplane is that the air pressure in the middle ear is different from the air pressure outside. When you 'pop' your ears, you push open the Eustachian tubes that connect the middle ear to the throat and make the pressure equal. No matter what the air pressure, the air still conducts sounds. The difference is that your ear drum moves a bit less if the middle ear pressure and outside pressure is different, thus why sound is muffled before you pop your ears.