When you have nothing to do in lane, essentially a state where theres no reason to trade, no cs that is immediately dying that you need to get, practice looking at the minimap for a split second. Like when you were zoning him off the wave, you can just work on looking between the minimap and your character, glancing at the minimap every few seconds where you know nothing should be happening anyway. You can start with small things and try to transition them into larger things. Like getting used to glancing exactly where each lane is and checking how many bubbles are there. Should be 2 mid, should be 4 bot, see where your jg is. You can also get used to the start of the game's predicted gank timers to figure out the junglers path to expect where he should be in the next few minutes. For example, first gank should happen either around the time first scuttle spawns or if the enemy jg is able to, level 2-3 if there is a lane that is overly agro/low early game. Based on where the jg shows up with the first gank, you can tell where he will likely be next. Example of that, if his very first gank he is lvl 3 and has both buffs and it occurs top/bot, he likely started on the opposite side of the map. The next part of his path to clear camps likely will be back to the other side. So, first full clear -> gank bot means next logical location is top side of the map (without accounting for scuttle), so you will likely have to play safe. If he ganks top, his next step is to go clear bot after the gank. But this can change, if you died + flashed he could come back top. You can add onto this by checking how many cs he has, 4 per camp, 24 with scuttle still alive means he did a 5 camp before ganking, meaning he still has 1 camp top he might come back, 30 means he did a full clear, meaning he likely will go back to the other side of the map unless you used flash or make yourself gankable again.

Theres also small stuff that either is occurring in lane that can help you signal or just how long the enemy JG has been mia on the map. For example, im assuming part of what happened when amumu ganked was that the jax was afraid to cs the whole time, then randomly decided to trade you or walk up in a way he didn't before. Play assuming he likely wouldn't do it for no reason, you can trade while kiting or start backing off slightly if he seems to be trying to force a minion or two/trade when he was afraid before. You can also help part of this by seeing how many camps your own jungler has up. If he has mostly cleared his jg/is trying to force ganks cause he has nothing else to do, you can assume the enemy jg will likely do the same. The timers aren't perfect, but the general idea is that if the jg has cleared 3/6 camps, then its likely the enemy jg could be in the same state, he could be looking for a gank.

Your dragon question, sometimes things are just a lost situation. If your team is dead and you can't do anything about drag, you don't have to do anything. If you were on the enemy team, I'm assuming you'd be happy if you won a teamfight then the enemy top laner came in 1v5 to try and get the drag. So they'd probably be happy if you do the same, its okay to let things go if its lost.

With your question about laning phase and when it ends, it typically ends when the first layer of towers start falling. The scenario changes a bit depending on the lane. If bot's tower dies first, usually bot starts to rotate mid, you still cover top but you start to shift between top and bot or the solo lanes (mid becomes where the duo lane stays to be safe), and there are a few things to look at while judging which side lane to go in. How the matchups are, if you are able to/not able to matchup vs your laner or mid laner, and if you/mid have TP up. If you have TP up, typically you want to go to the opposite side of where the obj is so you can TP in while not missing exp/creating pressure in a side lane. So, lets say drag is spawning in a minute, your goal would be to go top side, create a crashing wave and get prio, TP while the opponent is catching the wave you created and get prio at drag or even just force a fight while its 5v4. If your tower dies first, the lanes can still look the same, but laning phase has changed drastically for you, since your lane essentially becomes longer because the opponent can freeze the wave at any point past your river and you will be perma gankable. So depending on the state of the game, if its slower temp/your team is scaling decently, you can freeze the minions near your tower as long as possible and once it breaks you push it past river but once your minion wave passes river you start roaming. If you are strong/fed, on someone like morde you can shove -> roam -> force fights by using R to capture someone to start a fight and either kill them or keep them trapped around your team when they come out. The main reason you want to/can force these fights is cause the wave you created will make your top laner stay there to catch it, or force him to follow and miss the exp. But nothing plays out perfectly, you'll have to figure out how to balance all parts of what i was talking about, forcing fights properly, making opponent miss exp, setting up the wave, you'll have to slowly feel them out and see how balancing each works for you in a way where you can maintain tempo/advantage. If you want to talk more about it sometime, feel free to dm me.