While browsing groups in Dungeon Finder you will see the Mythic Plus Scores for each group's leader.
View Applicant Scores in Dungeon Finder
Tooltips will show current overall and per-role scores. Additionally, the previous season's overall score will be shown if greater than current season. If you register a Raider.IO account you can even have your Main's score show while on your alt's.
View Scores of Members in Your Guild
View Scores when Searching for Players in the "Who" UI
Sometimes you'll want to browse a player's profile on Raider.IO directly. Right-click to copy their profile URL and then paste it into your browser. This can also be used when targeting players.