I was wondering what scales one should know in order to practice or to know to have good knowledge of the fretboard and whatnot. Like.. what are the essential scales/All [If possible] that a guitarist should know? Which ones are essential to improvising and whatnot?
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You should first learn the shapes of the penatonic major/minor scale. This is the most basic scale. After that, you should learn the major scales, and all their modes, and natural minor. I'd settle for that for now, but after you're ready to learn more, you should learn the harmonic minor, melodic minor, and their modes.

With these scales, you should practice writing music, and improvising solos

You can search the lessons on UG, or search on google to find all this info.
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I would suggest learning the major scales first and actually learning a bit of the theory behind them. The major scale is essential, in my opinion, more so than the others listed as far as beginning guitar goes. The pentatonic shapes are only 2 notes per string and will come much easier once you have become familiar with the major scale patterns. I only say this because of the nature of your question. You seem to be a beginner and I am giving you advice useful to such. modestmouse911 is not incorrect but I think his order will only make things harder for you by throwing you into areas you are not ready for yet. Working in steps and building upon what you already know helps a lot with memorizing the fretboard and all areas of guitar. I hope this helps, good luck!
I would agree that your major and minor scales should be memorised before your pentatonics.
So my order would be...

Natural Minor
Melodic Minor
Harmonic Minor

Then you can get into modes and have a ball relearning all your scales 7 times over again :P
Everything's based off of the major scale, so that's a good thing to start with.

Then pentatonics, modes, blues scales, and minor scales (not necessarily in that order!).
You can learn all the scales you want but it wont help you memorise the fretboard.
Ive learnt all the modes of the major scale and can play them all over the fretboard, but I hardly even know what notes I am playing, so now I am going through and learning all the notes on the fretboard.

I guess my advice is learn the major, minor and pentatonic scales, but dont take them much further until you know most of the fretboard, and I think its a great idea to play the scales while saying the note names, that way you're killing two birds with one stone.
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