The easiest way to find someone else's wishlist is by receiving a direct link to the list from them. You can read more about how to share a wishlist here.
If you'd like to try finding the wishlist yourself, follow these steps:
Log in to your profile – or create one if you don't have one yet.
Click on the icon with two people in the top right corner.
Type the person's name in the search bar.
Find the person in the search results and click on their name.
You will now be taken to their profile.
Note: If the profile is set to private, you will need to send a friend request in order to access their wishlists. Learn more about how to add friends here.