A fun game show I liked watching growing up was Name That Tune. Two contestants would receive a song clue and then attempt to name the tune using the least number of notes possible. I enjoyed hearing a small number of notes and seeing if I could pick out the song. Even though the show stopped airing in the 1980's, it's still a fun and challenging game I like to play when listening to popular music.
I also enjoy playing Name That Tune on my guitar. If there is a song melody I really enjoy listening to, I like to see if I can pick out the notes and figure out how to produce these sounds. It's also nice to have some variety in my playing and have others attempt to guess the song.
Select your favorite song and see if you can pick out the hook or main riff of the song on your guitar. It's a great exercise to help you build up your chops! If you continue this approach with additional songs, over time you'll build up your repertoire which will give you material for creating your own melodies and songs in the future.