Showing passed questions again

Got it. You could do this with JavaScript and by storing an Array as a text variable in Storline. 
When the user skips a question, you would execute JavaScript to pull the Array and the question number from Storyline, convert the array from text to numeric, append the array by adding the question number to the end, and sending it back to Storyline as an updated value in the Storyline Array variable.

Next, on review of skipped questions, you will do the opposite. On trigger (probably a next button click) execute Javascript to pull the Array from Storyline, isolate the first value in the array and separate it into its own variable (removing it from the array), the sending the updated array and question number back to Storyline. You can use the question number retrieved from JavaScript to guide the navigation to the question that should be reviewed.