Unless you're going to do some sort of horticultural qualification, then it has to be down to practical experience plus a general interest.

I've been a serious gardener for the last thirty years and have acquired all sorts of (fairly limited) knowledge over that time.

My heart sinks when someone (not you) posts on this board wanting instant answers. Proper gardening takes time and effort. FWIW, my initial foray into serious gardening was as the result of befriending the mother of one of my DD's friends, whose parents owned a plant nursery.

Personally I'd ditch the cataloguing etc. A subscription to Gardeners' World magazine should be more than enough to nudge you in the right direction.