Emaj9 is built from E, G#, B, D# and F#. E is the root, G# the major third, B the fifth, D# the major seventh and F# the ninth. Said aloud, its notes are E, G sharp, B, D sharp and F sharp.
String by string, low to high, it plays E, B, D#, G#, B and F#. B appears twice in the main shape, and it is the chord's fifth. It runs from E on string 6 up to F# on string 1.
The open strings add notes to Emaj9 too. String 6 gives E and string 2 gives B. Your hand covers two frets, from 1 to 2. There is one more position, starting at fret 6.
Change only string 1 in Emaj9 and you have Emaj7. Inside Emaj9 sits a complete B chord, made of B, D# and F#. Moving to E, you keep two fingers down.
Emaj9 belongs to four keys. In E major it is the Imaj9, in B major the IVmaj9 and in G# minor the VImaj9. The rest appear in the key list.