>>41294679Slower than you would think, faster than any other game. Your best bet would be grinding Dynamax battles and catching a fast experience group pokemon with a decent amount of levels on it. The reason you Dynamax battle is because pokemon gradually receive less XP from weaker leveled pokemon and killing the "elite" pokemon in the area don't actually give great XP gains for the amount of time it takes to kill them + the risk involved.
Because it makes the math easier for me, lets assume you are trying to get a level 1 Cleffa to level 100. That takes 800,000 experience over all.
You receive 5 Extra Small Experience candy per Dynamax battle for 500 flat.
You recieve 1 Small Experience candy per Dynamax battle for 800 flat, overall 1300 per dynamax battle.
You occasionally receive a rare candy as a reward.
800,000/1300 = 615.3846, or 616 Dynamax battles for the raw XP candy needed to get a fast experience pokemon from 1 to 100. The number of attempts will go down a great deal for a) every level the pokemon has before you started to feed it candy and b) how many rare candies are dropped but I'm not interested enough to figure out how that would potentially average it out. Let's just say it will usually take over 100 dynamax battles to get a pokemon to level 100 with some variables thrown in.