# FORMA 1
felipe@localhost ~]$ loginctl
   SESSION        UID USER             SEAT
         1       1000 felipe           seat0
        c1         42 gdm              seat0

2 sessions listed.
[felipe@localhost ~]$ loginctl show-session 1 -p Type
Type=x11

# FORMA 2
[felipe@localhost ~]$ echo $XDG_SESSION_TYPE
x11
[felipe@localhost ~]$