Scholar is directly tied to your Arcanist level, so you won't have to level it again (and any progress you make on it will also count for Summoner if you want to pick that up). So it'll start at 30, or whatever level your Arcanist is.

For future reference for other jobs, the primary ways of levelling outside of MSQ are Fates, Dungeons and Roulettes, or Palace of the Dead. From level 30 onwards, PVP is also an option.

Good luck!