The notes of E7#9 are E, G#, B, D and F##. E is the root, G# the major third, B the fifth, D the minor seventh and F## the sharp ninth. Said aloud, its notes are E, G sharp, B, D and F double sharp.
String by string, low to high, it plays E, E, G#, D and F##. The root, E, shows up twice in the main shape. This shape leaves out B, the fifth. It runs from E on string 6 up to F## on string 2.
In E7#9, only one string rings open, string 6, which gives E. String 1 is not played. Your hand covers three frets, from 6 to 8. There is one more position, starting at fret 1.
E7#9 and C#m have E and G# in common. Dbm shares one position with this shape.
The notes of E7#9 do not fit together in any major or natural minor scale. Further down there is a song that uses it.