If asking others to pray for you an Obligation?
No
Does it glorify JESUS more because people share in his mediatorship or is He just as glorified without it because He is already perfect and GOD.
Jesus isn’t a “mediator”, He is God. You’re praying directly to him.
This also has nothing to with “glorifying” Him. He’s already in glory, He’s perfect, He’s God. If you want to glorify God, you just say “All praise and Glory to God” or you live in a righteous way so your life gives glory to God by your actions.
Also since it helps does that make it a sin not to ask for prayers?
Not necessarily a sin; would only be a sin if the reason you were not asking is that you were overly proud and saying “I don’t need anyone else’s help!” The sin would be your pride, not the fact that you didn’t ask for prayers.
Whether sin or not, it’s pretty stupid to not ask for help when it’s readily available from Mary, the saints, etc.
If your car broke down and you had to push it a few blocks to a gas station, and you saw some strong people standing around who were willing to help, would you tell them, “Thanks but no thanks, I can push the car myself” or would you let them help you and get the car there quicker and easier?