Model number (on the back cover):
A1876 on the iPad Pro
A2014, A1895 on the iPad Pro Wi-Fi + Cellular

Model number (on the back cover):
A1980 on the iPad Pro
A2013, A1934 on the iPad Pro Wi-Fi + Cellular
A1979 on the iPad Pro Wi-Fi + Cellular (China mainland only)
 

10.5" Retina display
Model number (on back cover):
A2152 on iPad Air (3rd generation)
A2123, A2153 on iPad Air (3rd generation) Wi-Fi + Cellular

Model number (on back cover):
A2133 on iPad mini (5th generation)
A2124, A2126 on iPad mini (5th generation) Wi-Fi + Cellular
A2125 on iPad mini (5th generation) 

Model number (on the back cover): 
A1893 on the iPad (6th generation) Wi-Fi
A1954 on the iPad (6th generation) Wi-Fi + Cellular

iPad (7th generation)
Capacity: 32 GB, 128 GB
Model number (on the back cover): 
A2197 on the iPad (7th generation) Wi-Fi
A2200, A2198 on the iPad (7th generation) Wi-Fi + Cellular