What is Sov +2 from builder?

[Feomatar]

Is it rank or gear bonus or what is it?

[Omegus]

Sovereign sets grant +2 mastery points to specific paths (the path varies between careers and their 2 sets of sovereign gear) . The option on the builder just gives you an extra 2 mastery points to play with but it's up to you to ensure the build is still valid.

[Feomatar]

Is this best sett in the game or we have same ilvl scenario sett?

[Sulorie]

Is this best sett in the game or we have same ilvl scenario sett?

No, there is no scenario set needed as sov set exists in 2 variants already. They are for many classes the best sets but not as full set, so +2 mastery will be irrelevant for many.