Go to Stories and hit search. Type in their username. If you are not blocked, their name will appear in the search window. If the name does not appear, then that means that you have been blocked or that they have left Snapchat entirely.
If you are looking for how do yk when someone blocks you on snapchat then you must check out the given reference guide below to know more.
When you open the app, click on your Bitmoji/story icon in the top left of the screen, click the settings icon scroll down to the very bottom of the list and …