This has been reported extensively elsewhere (see here, for example), but lemme point out the Pew findings on who is aware, and unaware, of the recent gigantic health decision by the U.S. Supreme Court. 

Who's clueless?  Survey says: young people. 

See the table below.  Among the youngest adults, 43 percent didn't know what the court decided.  As is the case with most forms of political knowledge, the accuracy somewhat increases with age and certainly the likelihood of saying "don't know" goes down.

Let's acknowledge that younger people are (1) less politically interested and (2) less interested specifically in health care given where they are in their life cycle and (3) are, yes, less politically interested.

Or, perhaps, they're less likely to guess?  There is research that suggests men are more willing to guess at a political knowledge question than women.  No evidence here of that.  Just making note of it.