Stan, a citizen of iowa, files a lawsuit in an iowa state trial court against jalisco farm supply, a texas company that sells supplies in iowa. the court has original jurisdiction because:

The answer is because this will be the first time that the case to be heard this is what you called the original jurisdiction of a court. This is the power to hear case for the first time, averse to appellate jurisdiction, this is when a higher court has the power to study a lower court's judgment.

It is the court where the Plaintiff, Stan, filed the lawsuit. 

Jurisdiction is set at the lowest court applicable and where the plaintiff files the lawsuit. Being the plaintiff is from Iowa, the Iowa court is where they must file the lawsuit. Being the defendant is a company in another state, the lowest level of court that can hold jurisdiction is the state court.