Sounds like adware on your device your using whether it's a pc or phone, since it keeps reappearing. Download Malware Bytes then scan to try and remove it with
what does it say? information helps us to give correct answers rather than guesses. thanks.!
Ok, let's get EXACT. What browser do you use, does the popup have a title, colored bar, any other icons etc on it. It sounds like a notification from a jobs site. Go into your browser notifications and turn them all off.