Em scale will fit in an Em progression, if it's not E, then it might be A,G or D ... just the same patterns.
If it's E, then you'll find it going from 12 to 15 , or 0 to 3 fretts
A you'll find it going from 7 to 8 , or 17 to 20
G from 3 ot 6 ,or 15 to 18
D from 10 to 13
These ain't the rules, but it's a good starting point.