Tomorow I have my first job interview for junior sysadmin. Any tips?

Chill it out
They won't bite.
If you don't know an exact answer to a question don't say "I don't know" but ask, ask and ask so you can build the answer from their input eventually. If you still don't know the answer explain that you are not that familiar with that topic yet but you look forward learning about it (But don't lie!). Questions are also a great way to show how you handle things, maybe explain how you would handle the situation in a real world szenario, but stay on topic!
Short precise answers, talk slow and clearly (force yourself a bit, helps against nervousness) and never forget: The interviewers are just humans like you and me, try having fun and show yourself open to the other persons in the room. Don't be afraid to speak, they will be your colleagues eventually - don't forget that.

Good luck! 🍀

Linux or Windows ?

@Kimmax Good to know, thank you.

@elgringo Windows

@mitea

Read/learn about PowerShell and Windows Sysinternals

Good luck