Which certification do you get after the 20weeks training as a 25b ?

You don't get any certifications. You have to take those tests on your own once your knowledge and experience level are high enough

None. You'll likely need Sec + at your unit but they'll handle it.

Since you are National Guard I would highly recommend getting a certification if you want to work IT on the civilian side. I personally recommend Sec+ seeing as its the preferred of the IA level 1 certifications. It may have changed but the school house will allow you to take a certification test before/after school hours, if you have completed all Skillport learning for that topic and a measure up test that can show that you are ready for the CompTIA Security+ certification test. It is not an easy certification so you will need to study, but very useful in the civilian market.