I'll be traveling to Prague soon and I was hoping to purchase alcohol at a reduced price. Can I purchase it in the duty free stores? (Are there restrictions in the Czech Republic on boarding planes with liquids (like in rest of the EU)?)
Airport Duty-Free stores are located after the security check points and before the boarding zone. As such, purchasing Alcohol would be allowed and carrying it aboard, assuming you will pass any other boarding requirement as well, would also be allowed. (Note, in at least the US, a lady's purse counts as a carry on, so if you also had an actuall (rollaboard) carry on, a package from a D-F store would most likely need to be gate checked. (or your rollaboard.)
You didn't mention it, but opening the bottle(s) of alcohol would at a minimum be discouraged and more likely prohibited. Without knowing your airline, I cannot look up any rules for you.
The other thing is that Prague, and the rest of the Czech Republic, is not only part of the European Union, but also part of the Schengen Area. So yes, the rules observed by the rest of the Schengen Area nations, and the EU, are the rules you must follow for Prague.
To be honest unless you are arriving here by plane then no, there is no good duty free. But alcohol is cheap enough, you can buy at tescos, lidl, aldi etc. Although the large tescos superstores carry the best range at a good price.
For boarding a plane you would only be allowed the standard 100ml bottles in carry on and would have to check the rest.
More importantly you might want to check what is the regulation in your destination country for import; for instance, absinthe, popular in CZ, is illegal in the US and Canada for importation.