Originally posted by Tele Master
So does this mean there is only one position to learn, you just have to know what key your in?

No. There are many positions for each scale. For everytime the root note appears on the fretboard, that's how many positions there are. You should at least know the positions that start on the top 2 stings (E and A), at least. Go back and look at the previous thread I replied to for ways to practice them.

Originally posted by Tele Master
If so, whats a good way to know what key your in for which mode?

When you're playing a mode, the key signature is usually written in the parent key. Like if you were playing D dorian, the key signature would mostly likely be C major. The only exception which is rare is when the root (of the mode) is matched with the key. Like C lydian over the key over C major (chord progression). Although you have to watch for the chord progression cause there can be some tension with come chords.

Originally posted by Tele Master
Most scales start on the root note, but Ionian for example, can start on the open E-string.

All scales start on the root. C Ionian can't start with an open E and still be called Ionian. That is E Phrygian. The root is the most important note, it shows you how to use that scale. Match the root of the mode (scale) with the key note or root of the chord, that's all. Simply application. This is why you learn modes seperately from their apparent scales.

Note: When you practice modes you shoould always keep the same root. Like C Ionian, C dorian, C phrygian, and so on. NOT C Ionian, D dorian, E phrygian. This will help you seperate their differences and end all the confusion.