Finding out antenna gain in 3-D space (azimuth and elevation)
The diagram doesn't provide any information about how the gain varies as a function of azimuth, but for many analysis purposes with most patch antennas you can just assume the beam pattern is symmetric about the boresight axis - i.e. provided your "azimuth" and "elevation" are defined with respect to the antenna orientation, just discard the azimuth parameter and look up the elevation into a table derived from one half of the plot you showed.

This will usually be within a dB or two, at least within the region of the main lobe (approximately the -3dB beam width region indicated in red). Anyway in real life the gain pattern is influenced to at least that extent by the surrounding geometry of whatever it's mounted to; those effects can be simulated but would require more data on the antenna construction to do so.