The Dimensional Gates Demo has increased the Exp earned off each enemy and therefore pushed grinding to higher levels much easier. The tutorial tomb still has a low Exp earned for the rats, but once you open up the Forest of Fayne, you can start grinding there. The Volcano at the end of Doller's chapter is one of the best places to grind if you want to get her and the Shadow Squad up to level 12 or higher easily.
Yeign's chapter still has no Exp earned for the creatures that leave Remains that can be exchanged for items, but outside of Navon and in the Mines, you can grind away.
Dimensional Gates Demo and Full Game Have Added Grinding: Due to User Feedback
Source: Steam Community (opens in a new tab)