Knock sensor problems, wont accelerate

Hello everyone, this is my first time posting on here, and unfortunately its due to a problem. So i recently bought a 2012 Peterbilt 587 with 480k miles and its been giving problems of the knock sensor.

Heres the run down:
So I was dropping off and I turned off the truck for about 90mins, then I was about to leave and i turned it on and the dashboard lights were on---check engine light, and the check engine light with the wrench on it, as well as some other lights.
As i tried to accelerate, it wouldn't. And the rpms wouldnt rise up either when i would give it gas. So i called a mechanic over, they ran the diagnostic tool on it and they told me it was the knock sensor that was going bad. So they cleared the codes and the truck ran fine for another 3 trips of 1500 miles each.
But on that 4th trip, it happened again. Another mechanic came and told me the same thing, neither of them told me the codes, but im on here to ask if that could be the problem.
And if so, where is the knock sensor on this truck. I know how to work on cars, but on a truck like this, i dont have any experience.
If its not the knock sensor, what else could it be? Some other drivers said it could be something about the DEF filter, but i dont even know what that is. Sorry for the noobness guys, but im just on here looking for help so this wont happen again and i could be on the road worry-free of this happening again.

Thanks in advance. In regards to buying a diagnostic tool, if you guys can recommend one, i'd appreciate that too.

 

First of all, thanks to both of you guys for responding. Secondly, would you say i would need to replace both or just one (if so, which one?)?

Thank you again.