You get into Sapper Companies by being enlisted into one. The recruiter is going to be putting you into a vacancy in a unit so if you want to be in a Sapper Company, you're best bet is to ask for a Sapper Company. You'll be a 12B (Combat Engineer) which is also going to be the primary MOS in a MAC and Route Clearance Company. Sapper School attendance is unlikely, so you should be prepared to never have the opportunity to go. Not sure if that's important to you or not, but don't go for the MOS assuming you're going to get the specialty school too. Good luck.