Hi @LocarioDJ,
Welcome to the Community, and thanks for reaching out with your questions. I’ll be happy to help.
- Does djay Pro AI on iPad suggest compatible songs by key to the song playing? => YES
To see the compatible songs by key, you’ll first need to use the Sort option to sort by key in the current playlist, as shown here:
Then you’ll see a navigation bar on the side of the playlist that you can use to find the key of the currently playing song in the sorted list:
And from there you can navigate to the currently playing song and compatible songs, by key:
In addition, you may want to check out this already existing Community thread, as it is closely related, and is a suggestion for a more powerful filter showing songs by compatible key.
- What is the best way to sort music in djay?
In general, there’s not a one-size-fits-all approach to this. It really depends on your personal preferences and typical flow as a DJ. That said, I would like to point out that making use of djay’s My Collection library source to create your own playlists, smart playlists, and playlist folders may be helpful in the future if you feel limited by your current approach with parent folders/subfolders. You can find out more about the My Collection source and how to use it in the user manual here:
- Is there a way to write comments for the songs? => Not yet
Here is the related Community thread for this popular request: Implement a comment section.
I hope this information is helpful! Let me know if you have any other questions. 
