Hey so I personally don't think you should use TuSKe as it break's other plugins and is very unreliable and easily can be manipulated.
I also don't think you need skript gui, you should use vanilla gui using Skript I believe.
an example is something like this;
command /buy:
trigger:
set metadata tag "storegui" of player to chest inventory with 3 rows named "&9&lStore"
set slot 0,1,2,3,4,5,6,7,8,9,10,11,12,14,15,16,17,18,19,20,21,22,23,24,25 of metadata tag "storegui" of player to gray stained glass pane named "&f "
set slot 26 of metadata tag "storegui" of player to glowing barrier named "&4&lCLOSE"
set slot 13 of metadata tag "storegui" of player to glowing feather named "&b&lRanks"
open (metadata tag "storegui" of player) to player
on inventory click:
if event-inventory = (metadata tag "storegui" of player):
cancel event
if index of event-slot is 26:
close inventory of player
stop
if index of event-slot is 13:
send ""
send "&7If you would like to purchase a rank, please click <link:store>&9&lHERE<reset>"
send ""
close inventory of player
stop