When your retention window comes up, what can you ask of the retention nco? Can you ask for multiple things like reclassing and sapper?

You can ask what if any MOS’s and or soecialty training that is available, including assignments. You can inquire as to the Guard, reserve and active duty. But you will need to pipe in recruiting and retention from the other two as well. The world is your Oyster.

You could ask your gaining unit for Sapper if you are reclassing to 12B, 12C and 12N.
You can't get an ASI school "guaranteed" in a Guard extension, you can only get the reclass and bonus or SLRP guaranteed.
And Sapper seats for the Guard are very limited every year, and Sapper school is limited to 12B, 12C and 12N.
Due to those very limited seats, those Engineer units will likely have an OML for Sapper, and you would be added to the bottom of the list as the new gain.

Just me, but I'd inquire about the reenlistment bonuses I read about last month (May 2023), some upwards to $20,000 for eligible Soldiers reenlisting for 6 years. I believe you have to be DMOSQ and have less than 13 years of time in service.
$20,000 bonus for 6-year reenlistment.
$12,000 bonus for 4-year reenlistment.
$5,000 bonus for 2-year reenlistment.

*Reenlistment bonuses are taxed like regular income ☹