- Vassals/Client states = land force limit
- Marches = nothing
- PU = nothing
- Trade company = 1 naval limit per 2 provinces, zero manpower contribution
- colonial nations = naval force limit
- protectorates = nothing
Subjects don't directly give bonus manpower, however they (trade companies aside) can help you in battles allowing you to save your manpower (though protectorates are limited in what kinds of wars they can fight), since they have their own pools of AT LEAST 10k manpower to build troops from even if they only have 1 province.
So there's no actual direct bonus, but you do "get" extra manpower by having subjects, hence why France having his vassals pre-integrated in recent patches was seen as a huge nerf since now it has to fight it's wars with only it's own manpower pool, and why most people prefer to keep the HRE on the 2nd to last reform, since you keep all the reform bonuses and have the entire HRE as a massive vassal swarm that doesn't take up relation slots and 4-5x the amount of manpower pool worth of armies then you'd have from uniting it and can only compare their individual strength vs yours, instead of all vassals relative to you.
Trade Companies unlike all the other examples aren't separate countries and are instead provinces you retain control of but add to a trade company charter to gain a huge boost in local trade power and the ability to ignore unrest from religious or cultural differences, but at the cost of all manpower you would've gained and half the taxes and a flat .5 naval force limit per province. On the other hand, it's most likely you'd have had a minimum 75% autonomy and wouldn't have gotten much anyway, where as the province isn't locally penalized from the overseas autonomy when it's in a trade company since the province is considered under local management