You write the electron structure like this.

Question

1s2 2s2 2p6 3s2 3p6 3d10 4s1 is the neutral Cu atom.
Remove the two outside electrons to make the Cu^+2 ion. That leaves us with
3d9 as the outside and since that is an odd number, one electron must be unpaired. And you will note that many Cu(II) compounds are colored.

So for CoCl2·6H20 the electron configuration is [Ar]4s2 3d7 because Co is 2+ so would the unpaired electrons be 3? is that right?

Answer 1

Yes, it has 3 unpaired electrons BUT 4s2 are missing for the Co^+2 ion in the compound CoCl2.6H2O. You wrote the electron configuration for the neutral atom.
Do you know how to almost without thinking write the 3d electrons in the 3d transition series. It's the DrBob rule.