Nikon Z7 II has a 46.0MP Full frame (35.9 x 23.9 mm ) sized BSI-CMOS sensor and features Dual Expeed 6 processor. On the other hand, Nikon Z5 has a 24.0MP Full frame (35.9 x 23.9 mm ) sized CMOS sensor and features Expeed 6 processor.
Nikon Z7 II's sensor provides 22MP more than Nikon Z5's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Another difference between these two cameras is that Nikon Z7 II's sensor lacks anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the Z7 Mark II and Z5 sensor size comparison.
Nikon Z7 II and Nikon Z5 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 Nikon Z5 has 88% larger pixel area (35.51µm2 vs 18.88µm2) compared to Nikon Z7 II, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.