Has someone made any progress on importing transaction from jGnash?

especially for investment transaction?

I've never heard of jGnash until now, and I'm not aware that any work at all has been done on importing from it. If it can export transactions as OFX or QIF, then import should just work, or perhaps might only need minor tweaks. If it can export as csv, then import should be possible, although for Investments, I suspect you would need to set up the accounts and securities first. Without knowing more about their native storage format, I couldn't begin to guess what effort it would take to import directly from that.