I was injured in an auto accident as a passenger in a work truck (off company time, on the way to the job site), what am i entitled to?

If this accident happened in Iowa, and if there was contact between your vehicle and the semi, you may have a claim for uninsured motorist coverage under your policy or the policy of the vehicle you were riding in. If there was no physical contact, you may still have a claim unless the policies have a "physical contact" requirement for uninsured motorist claims. The Iowa Supreme Court has held that these clauses are enforceable.

Although I can't tell from your description, you might also have a workers compensation claim and  a claim against the driver of your vehicle.

Your injury sounds very serious, and it is difficult to answer your question fully in an email.  I would suggest that you call an attorney as soon as possible. Most attonreys who handle these cases do so on a contingent fee basis and will speak with you without charging a fee. The statute of limitations for any personal injury claim is two years in Iowa. (The time periods are different for a workers compensation claim; you should discuss them with an attorney.)