The Right Answer

I recommend using Math Strategy here. In fact, you can use the strategy in TWO different ways here:

Way 1: The phrase "Far from" indicates that the two ideas in the sentence contrast each other. The first idea states Jefferson is "skeptical but enlightened," a positive idea. Contrasting with that idea, "historians of the 1960s must view him negatively -- essentially the opposite of "enlightened." Looking at the choices, doctrinaire is the best fit.
Way 2: The comma after "thinker" indicates that the two ideas support each other. To the right of the comma, we see that Jefferson was "eager to fill the young with his political orthodoxy." He even "censored" ideas he didn't like. This is clearly negative. In the blank, we could guess a word like "domineering." Again, doctrinaire is the best fit.

The Wrong Answers

an adventurous: This choice contradicts the logic of the sentence because "adventurous" has a positive connotation.
an eclectic: I would argue this choice contradicts the logic of the sentence. If Jefferson were an "eclectic" thinker, he wouldn't have been "orthodox" or "censoring" ideas.
a judicious: This choice contradicts the logic of the sentence because "judicious" has a positive connotation.
a cynical: This choice has no evidence. The sentence gives no indication of Jefferson's pessimism or optimism levels.