The maj9 is also named major ninth
Use Δ9 instead of maj9
Use ^9 instead of maj9
A maj9 is a Major chord
How to construct a maj9 chord?
Use the following intervals in any order to construct this chord. Start on a specific note on which you want to construct this chord from (for instance the note "C") and calculate each interval on top of it. Afterwards, you will be able to play it on your instrument.