In all the years and countless hours I've poured into this game, periodically returning to play it out of an implicit desire to satisfy nostalgia, I've only ever learnt x1 technique at a time after battle.
In my experience, your digimon can only learn one per battle, and there appears to be no direct or indirect indication that your digimon can learn anymore than that at a given time.
Aspects that may improve possibilities:
- A relatively high brain stat value - it's no surprise that your
digimon needs to be smart to learn something.
- Successfully guarding against a given technique - in my experience
this seems to improve the chances of picking up that technique.
It's unfortunate that the advanced techniques are unlikely to be encountered naturally more than once or twice. It means you are subject to slim possibilities of learning these techniques through brain stat training (since you can't pick up any techniques from tournaments either).
Giromon's techniques and other opportunities to learn them:
- DG Dimension (Machinedramon - Back Dimension / Infinity Mountain)
- Delete Program (none)
- Reverse Program (Tekkamon - Greyloard's Mansion)
Unfortunately, I am unable to provide citations on any of the aforementioned claims as there appears to be no official reference or guide that I'm aware of. These are wholly based on personal experience - an accumulation of hours that extend well into the triple digits.