Where does dividend income show for brokerage accounts?

If you select Simple Tracking, you're telling Quicken that all you care about is the account balance, you don't care about what happens inside the account. This works best with things like tax-deferred retirement accounts, where the transactions inside the account don't affect your finances. But for a regular brokerage account you do care about the individual transactions because they are potentially income (and possibly taxable as well) so you should select Detailed Tracking.