External GPS for Use on iPad Air With Navionics and AquaMap apps

With absolutely no information about your iPad model - or installed version of iOS/iPadOS - it’s difficult to provide definitive information.

WiFi+Cellular models of iPad have built-in GNSS/GPS capabilities - and can be augmented with an external GPS receiver (e.g., BadElf, Garmin Glo). WiFi Only models of iPad have no GNSS/GPS - and therefore require an external GPS receiver for accurate location services.

External GPS Receivers that can be used with iPad generally connect via Lightning, or via Bluetooth.

Your description implies that you have the cheaper WiFi Only model - that lacks internal GNSS/GPS.

Both BadElf and Garmin Glo have good reputation.