what are the charges on the metals?

You can do it one of several ways.

1. Look at the periodic table. Mg is in group II. Mg is +2.
2. Look at the sulfate ion. If you've written very many formulas you know sulfate (SO4^2-) is -2. Since all compounds are zero charge, then Mg must be +2 to balance the -2 of sulfate.
3. S is in group VI. It is +6 (but you can't use this every time for S because S can be +4 and -2 as well as some oathers). O is -2 and there are four of them for -8 total. -8 from O and +6 from S means sulfate must be -2. Then Mg must be +2.

So, for NiSO4*6H20 the charge is +2, as well as for CoCl2*6H2O?

Or does the H2O play a role in the charge of the metal?

No, as you already know, I'm sure, H2O is zero; otherwise you would get zonked every time you took a drink of water. H2O is a compound and all compounds have a zero net charge (but the oxidation state of H in H2O is +1 for each and -2 for O).

You are right, both Ni and Co are +2 IN THOSE COMPOUNDS.

okay, so in FeCl3*6H2O the charge would be +3?

for what? for Fe in FeCl3.6H2O, yes, +3.

okay. Is it okay if I post some questions with my answers and you can check them to see if they're right?

Sure. Make it a new post at the top of the page.