Never done one myself but "hard" is a relative term, lol.
It looks to be just wrench work, wiring harness does need to be disconnected.
Take lots of pictures if it's your first time, those vacuum hoses and some wiring should be labeled before removing.
Yes, removing the lower intake would be required to change knock sensor.
Yes, regular gas would always ping/knock in a 4.0l SOHC, it has 9.7:1 compression, when an engine gets above 9.4:1 it will ping on 87 octane.
That's why they have the knock sensor on these, it retards spark timing when knock/ping is detected.
If you can get your hands on an ODB2 scanner then you may want to view the spark timing while driving, spark should retard BEFORE you hear the pinging, the fact you hear it could be because knock sensor is bad, but it could be spark is being retarded as much as possible but engine is still pinging from carbon build up or another reason.
It would be worth a look before pulling the intake.