Shutdown bitcoin-qt during reindexing? I started bitcoin-qt with --reindex and pruning on.
Can I safely shutdown and restart?
If yes how? Do I have to pass --reindex again or will bitcoin-qt remember and continue from where it stopped?
Can I safely shutdown and restart?

Yes.

If yes how? Do I have to pass --reindex again or will bitcoin-qt remember and continue from where it stopped?

No, Bitcoin Core will remember that it was reindexing and continue the reindex.