How can I have a secure wifi in flying j truck stop

Assuming they provide a generic public wifi, just use a VPN. While there are free ones, the most reputable ones are subscription service based, like NordVPN.

Using their connection I don’t think you can.I don’t know enough about VPNs to know if that would work

If you need security maybe you could look into a Mifi or other item, which is your own portable wifi hotspot that you would connect your device to. It’d cost you a cellular data plan though.

Or if you’re a professional driver see if flying J has any accommodation for drivers that need a bit more security than an open hotspot.