vape juice should be smoked in a vape rig ... "electric vaporiser", "sub ohm tank", etc the terminology is varied and a bit specialist. Pictures are worth kilowords so here's a reasonable video that goes into details about one set of components they find works well, but most vaping tanks and mods should work fine
As for dosing, the good thing about vape juice is that you can just take a short puff to see how it feels, then take more longer puffs to explore the different dosages. It's also a very outdoor and sharing friendly method, as you don't need to worry about handling small amounts of precious powser in a breeze!
Downside is that, depending on the strength of your juice, you may need to take in many long puffs to completely leave this reality... if that's your goal
edit: I should add that, personally, I use a vaporesso veco tank with euc 0.3ohm SS coils on a geekvape aegis solo mod ... (see how the jargon piles up quickly!) and, unlike the author of that video, haven't experienced any problems. But then I've also not really gone for it and taken multiple ten second pulls that might show up any wick feeding problems either.
Further edit: regarding dosage, you really can't tell how much you're getting with vape juice, you could guesstimate after the fact if you know what concentration of dmt you had in the juice and dividing by the number of vaping seconds it took to consume it all. But there's no real way to reliably map puffs to milligrams beforehand IMHO. So I recommend using bioassay and just starting small then working upwards in terms of puff duration and power applied by your mod box.