Re: Cloned repository to use programe locally. How can I check whether everything I downloaded is free?

> Could the repository contain proprietary blobs?

Yes. The repo owner might be violating the GPL. Or be the actual copyright holder of the GPL'd code and thus not bound by GPL's terms.

> If so, how can I check?

No easy way. Ideally, one would need to check each file manually. Sometimes a proprietary blob might even be smuggled as an array of numbers in a source file (it happens e.g. in a certain kernel named Linux)