I would tell your coach you are planning on attending the clinic.
Not so much ask permission, more just inform. If the coach has serious reservations about it, s/he could then ask you not to attend, and then give you reasons why. If you "ask" it leaves a much bigger space for him/her to say no without a good reason.
I think, based on the "rules" of the skating world, it would be bad form to go to the clinic without your coach knowing.
What is the litz technique? I'm curious as to why guest coaches would be told they cannot work on jumps.