I'm having a bit of a problem. When i signed up for my bass lessons, my instructor assumed that i knew the basics so he instantly skipped to more challenging stuff. So now (a year later), im stuck with the problem that i can play very well, slap, tap, harmonics, mute, everything like that...EXCEPT I CAN'T READ. what's a good way to learn the notes on the fretboard and to read?

this isnt a really good way to learn the bass lol...
First learn this. A,Bb,B,C,C#,D,Eb,E,F,F#,G,G#. It never changes. After that it is just a matter of knowing a note at a certain place(where you tune is a good start). Then the pattern just repeats itself. As for reading music, they teach that **** in grade school. Every Good Boy Does Fine, and on the bass it's FACE. The sharps or flats are marked right by the cleff.
Well learning the fretboard should come to you quicker than sight reading, so ill just help with the reading music:

in bass clef (what you'll always play in as bass guitar): you have 5 lines and 4 spaces in between, it actually, from low to high, goes GBDFA, and in the spaces it is ACEG. What the guy above did is pointed out treble clef.

he's right about the key tho, its marked in the left beside the clef sign. Assuming you're in concert band, you'll have a lot of pieces in Bb Major, (2 flats) so try to get a good understanding of that key.

And the rythmn aspect of sheet music shouldnt take long to learn (at least not the basic quarter/eight, etc. ). Only with maybe triplets, off beats, etc, you might have a problem, but for just starting out, 98% of people have problems with sight reading the notes as opposed ot the rythmn.
I have found that bass players are usually better at triplets and offbeats etc., because of the way that the bass follows the drums. You are probably decent at it and don't even know it. If you did have a drum machine or someone who is willing to just play the drums while you jam, I am sure that would help your timing.