Let me guess. The battle you were stuck on in Chapter 2 was at an execution site of some sort.
YEP! I fought that battle over and over and just couldn't cut it. I even looked at a FAQ for tactical tips and still couldn't do it. I simply couldn't do enough damage to the enemy and I'm pretty sure that at that point I couldn't go back to level up at all because a lot of the map is closed.
There's one spot you can grind in if you needed it but it's a pretty terrible map to grind on given the map's layout. The best solution to that particular fight is to break/steal weapons or aim for the arm.
The engineer is a pretty damn awesome job given it's utility and range.
It should be noted that FAQs for this game are typically pretty damn terrible given that they either expect you to sperg out on getting all the gamebreaking abilities as soon as possible, or tell you to sit in a corner and abuse repeatable moves to grind Exp and JP (or in one particular case temporary AT and Speed) in the most tedious way possible.
As for what you should do with Ramza, it doesn't really matter that much. As long as he has fairly good damage output and a reliable means to heal himself for a goodly chunk of HP per heal he should be fine. You could keep him in his basic job even, given the fact that his basic job is a unique and actually pretty damn good in stat gains and abilities (later on). Honestly Knights aren't really all that good in the long run given how much of a one-trick pony they are.
Also remember that whenever an ally performs an action, all of your fielded characters gain a percentage of that JP as well. So don't be afraid to spread your jobs out between your characters. You may really need that extra JP someday.