Is there sim tray of ipad 8th gen?

If you have the cellular model version of the iPad, there should be a nano-SIM tray on it.

The SIM tray is located on the lower right side of the device. To insert a SIM card, insert a SIM tool (or any pin) into the small hole to eject the SIM tray. You can refer to the image shown on this page: Remove or switch the SIM card in your iPad - Apple Support

Only if the iPad is a wi-fi+Cellular. A wi-fi only iPad will not have a SIM tray.