Where can I insert the Sim on iPad 5th generation

If your iPad does not have a SIM slot, then you have a WiFi Only model of iPad. WiFi Only models do not have any Cellular capabilities - and hardware cannot be retrofitted. WiFi+Cellular models of iPad do have a SIM slot - and recent models also support eSIM.

Remove or switch the SIM card in your iPad - Apple Support

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

It is not possible to change or modify the internal hardware components of an iPad.  Whilst a WiFi Only iPad cannot be transformed into a WiFi+Cellular model, you can use the hotspot feature of a mobile phone - or a Cellular Broadband Router (often known as a MiFi Router) - to access Cellular networks.

How to set up a Personal Hotspot on your iPhone or iPad – Apple Support

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Remove or switch the SIM card in your iPad - Apple Support

only the cellular models have a sim card slot, wifi only ipads do not and can't be made into cellular ipads