What are the technical solutions to measure $\ce{CO2}$ emissions?
In addition to satellite measurements of carbon dioxide, there are numerous ground based stations that also measure carbon dioxide: Italy, Hawaii, Australia, just to name a few.

If you want to catch carbon dioxide emitting cheaters, a dense network of such ground based stations would be needed around the world. The measurements would need to combined with meteorological data, particularly wind directions and strength. I imagine this would also require significant computer modelling to analyze all this data in a timely manner. This would need to be operated by a totally independent organization with lots of money. This will be difficult to achieve.

Alternatively, and probably more costly would be to have a constellation of satellites in geostationary orbit around the Earth constantly measuring atmospheric concentrations of carbon dioxide. As with the ground based stations, the data would need to be combined with meteorological data and processed via a computer model.

Monitoring compliance will not be cheap or easy.