I understand what topology is, but I need some practice to get even better in it.
I always find this difficult to answer because only you know your skill level. Some objects have a lot of cuts or curved surfaces, which is a bit more difficult. But I had to think of Jonathan's post right at the beginning, so maybe that appeals to you
https://cgcookie.com/posts/top-3-things-every-beginner-blender-artist-should-model?playlist=fek8wv
I would suggest you take something from your surroundings, then you can take a close look at it and hold it in your hand. This makes things a lot easier. For hard surface models, you can start with a keyboard or tools, pliers, a cordless screwdriver or something similar.
Or just have a look at the Weekly Challenges and choose something from there. Just go to Commuinty at the top, set the filter to “CGC Modeling Challenges” and have a look. I'll try to link it below
Thank you for some ideas to model, I will walk around and find something to model from.
I'd say start simple and little by little build up to complexity. And complex doesn't necessarily mean a huge robot, it can be a bottle of detergent, that thing has some funky ultra tricky shapes:
But if you want to go all the way, a car is always a mega challenge. Anything that has smooth curves yet sharp shapes is tough.
Mechanical pieces are always a go to as well:
The intricate shapes that flow into one another makes those things a headache.
If you're trying to understand topology better I recommend reading this site: https://topologyguides.com/
If you want something to practice topology then I recommend following this course: https://cgcookie.com/courses/blender-mesh-modeling-bootcamp
It's pre 2.80 user interface so there are differences in hotkeys, but that's not the important thing. It is a great way to learn topology.
As to Omar's suggestion there is this playlist, I haven't watched these and it's not my playlist. https://cgcookie.com/playlists/604-class-vehicle-modeling-with-blender-bc3-1806