Finding out if someone blocked you on Snapchat is not difficult. Just search for their profile, and if you can't see their "Snapchat best friends emojis" but they have sent more than 50 snaps, then they have probably blocked you.
You can also send a Snapchat to them and see whether it ever gets received.
If a few days pass and the icon doesn't change to received or delivered, you know that you have been blocked for sure!