See your product manual. Its must be written there how much water needs to be added. Then calculate for your desired concentration accordingly.
We add the indicated amount of water first to make the stock solution. Then we add 20 microliter of the stock in 180 microliter DEPC-treated water, generally.
Here is a link of nmol to uM conversion http://www.endmemo.com/sconvert/nmol_lum.php. In your case if you dissolve your 35nmol lyophilized primers into 1ml of SDW, the concentration is 35uM.
I prefer using TE buffer rather than water for preparing stock solution. The working solution can be prepared by further dilution to any concentration we desire.