1. Tsk is an abbreviation sometimes used for Task.
2. Sounds tsk or tsk-tsk denote disapproval; similar to tut or tut-tut. Below is an example of how this could be used in chat.
User 1: How do you format a drive?
User 2: You're a technician and you don't know how to format a drive?
User 1: Yeah I know. :(
User 2: Tsk-tsk!