I can’t find the SIM card on my ipad

All models of iPad are available in two principle variants - these being WiFi Only and WiFi+Cellular - each of the two being offered with different internal storage capacities.

WiFi Only models of iPad have no cellular hardware or a SIM slot. Only WiFi+Cellular models of iPad have Cellular capabilities.

Set up cellular data service on your Wi-Fi + Cellular model iPad - Apple Support

WiFi Only models also lack GPS functions - as GPS is an integral element of the Cellular chipset.

Only a Wifi AND cellular data iPad model will have a SIM card tray.

The SIM tray would be found on one of the long sides of the iPad.

Best of Luck to You!