Canon 1D X II has a 20.0MP Full frame (36 x 24 mm ) sized CMOS sensor and features Dual DIGIC 6+ processor. On the other hand, Canon 1D X has a 18.0MP Full frame (36 x 24 mm ) sized CMOS sensor and features Dual Digic 5+ processor.
Below you can see the 1D X MII and 1D X sensor size comparison.
Canon 1D X II and Canon 1D X have sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Canon 1D X has 11% larger pixel area (48.21µm2 vs 43.29µm2) compared to Canon 1D X II, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.