Yes, people typically speak some English in Prague. It’s a huge tourist destination, and as English is the international lingua franca, it makes sense that proprietors here would know the language.
However, you shouldn’t expect to find English speakers outside the big cities. If you’re going to leave the city and head to smaller towns and villages, the locals will likely speak Czech.
You may also find German and Russian. As there are no guarantees, it’s a good idea to have a translation app or phrasebook at the ready in case there’s no data or WiFi.