Measure the offset, center hole diameter and bolt circle.
To measure the offset, lay the wheel on the concrete and measure up to the back (mounting) face of the wheel. Turn the wheel over and measure again. If there is no difference, then the offset is 0. If there is a difference, the offset is 1/2 of the difference. I don't remember for sure which direction is positive offset, but the wheel supplier should be able to tell you if you give them the dimensions.
The bolt circle is the diameter thru the center of the bolt holes. Just measure directly across from center of one bolt hole to the other. Since you have six bolt pattern, it is easy. Five bolt patterns are tougher.
Note that the wheel I suggested has 0 offset.