You can access all your pinned questions on the Analytics page. To view your pinned questions, first tap on the Question Table at the top of the Analytics page, then on the "pin" icon. See the screenshot below:

You can also filter your pinned questions in the Question Bank by selecting the Logical Reasoning section and then typing "+pin" in the filter box. See the screenshot below:

The pin feature is not available for Logic Games and Reading Comprehension problem sets. This is because Logic Games and Reading Comprehension problem sets are done on a per-game/passage basis. Pinned questions only show up for Logical Reasoning, because Logical Reasoning is done on a per-question basis.