how many people can I see during a zoom call on an ipad with a 10.2" screen

As many as are connected. Zoom will adjust the video size of each participant so all fit in the gallery view screen up to 49.

If there are more than 49 participants, Zoom will generate extra participant pages to see the rest of the participants.

This behavior is un-related to the physical screen size of the device.

See here: https://support.zoom.us/hc/en-us/articles/201362323-Changing-the-video-layout-Active-Speaker-View-and-Gallery-View-#h_ac952845-ed43-4884-8263-4356f98e26f3