Which valency should i use in electroplating? ik or ous? Why?

I presume you don't mean 'ik' as you say but 'ic'? .. otherwise it doesn't make sense. The ic and ous are old fashioned terms that modern chemistry has replaced with the IUPAC system.

It really it depends on exactly WHAT metal you are trying to plate

so for copper you would use Copper(II) salts [ old name cupric]

for tin you would use tin(II) salts .. [old name stannous]

with zinc there is no zincous or zincic , just one set of zinc(II) salts

so there is no clear cut answer, it depends on which metal you want to plate. Unfortunately you haven't given that info.