Honestly, I just used Sonic as an example to see if anyone knows if it's still relevant. I don't think Sonic is as well known now as it was, but I wasn't sure how well it retained its popularity due to things like the show it more recently started and some of the mobile games. I actually had typed a section including this part, but decided to leave it out to see if anyone could supply some information about that.
ehhhh, most likely just as many or more people (and youth) are aware of Donkey Kong versus Sonic. Bear in mind Donkey Kong is in Mario Party, Mario Kart, Smash, etc.
If anything the only reason Sonic's presence in the minds of youth still is strong is due to MEMES and the hilarity of Sega screwing the series up.... if you look up Sonic in Youtube the top results are going to be parody videos or comedy playthroughs of like Sonic 06.
I would be surprised if Sonic is a more recognized character than Donkey Kong. the majority of Nintendo mascots seem to be fairly universally known across all ages.