Hi Kelly!
Interesting question! The tsk (pronounced tisk) is most often expressed as a double tsk, tsk. It's an expression of shock, disappointment or annoyance.
For example, "of all the people, you were involved? tsk, tsk."
"You both knew about it? tsk, tsk."
Native speakers of English often make the "tsk" sound by placing their tongue on the roof of their mouth and drawing the tongue down in a sucking motion to get a kind of spit-sucking sound. It's tough to describe; I guess that you'd have to hear it.
Good luck with your learning goals.