How to show a list of value if 2 conditions are met?

Hello everybody, glad to be part of the community.

I’m a beginner so my question is probably fairly easy to answer.
I’m creating an app to help teenagers to choose the studies they should pursue depending of their personality.

Page 1:
The user choose between 100 skills the faster they can, each one on a checkbox input.
Then click on “Validate”
Choices are saved under a database “skills1”
Then Page2 is loaded.

Page 2:
The user choose again between those 100 same skills, each one on a checkbox input. But this time they take their time.
Then click on “Validate”
Choices are saved under a database “skills2”
Then Page3 is loaded.

Page 3:
I would like to present the user only the skills he has previously selected in both skills1 and skills2.
So if he selected a skill on the page1 and then again in the page2 I would like it to appear here on page3.

Then the user would select a list of only 10 skills out of those preselected skills.

I tried some things but I kind of blocked and can’t find a way to do it.

Anyone care to help ?
Thanks

Hello,

Nobody ?