Not nearly enough information was given to allow for a valid suggestion.....
That won't stop most of us! This is the internet, where everybody is wrong, and free advice is still worth exactly what you paid for it!
Speaking of wrong opinions and advice that's worth what you pay for it....
The way I handle these threads is to try and toss out 3 to 5 suggestions, usually based on price.
There are certain qualities I think of when somebody says "truck knife". To me, the phrase implies:
They already have most of their other cutting needs covered, so the truck knife is the implement that gets used when something unexpected happens.
It may spend years in a box or a sheath.
It may get lost or stolen from the truck.
The "truck knife" should be plenty sturdy. It may get used as a hammer, shovel, prybar, and whatever else we all know we shouldn't do with a knife.
It should be either stainless or coated, because I can't tell from way across the internet, how much TLC this knife is going to get. It may rattle around in the bottom of a bed box for years.
It should have a good sheath. It may need to venture out away from the truck with you, for a good distance, in bad weather.
At the same time, it can't be too expensive, because there is a real possibility that all the care and precaution in the world will still not bring it back to the truck at the end of the adventure: sometimes, it's a choice between you, and the tool.