For example, Schnorr signature is pretty similar to El-Gamal. And everywhere where Schnorr signature is explained (for example - on Wikipedia), there's said that there's Schnorr scheme which is actually interactive proof of knowledge scheme (or identification protocol). Then, applying Fiat-Shamir transformation, we get Schnorr signature scheme.
At the same time, there are no mentions about El-Gamal interactive/non-interactive proof of knowledge El-Gamal protocol. And nobody mentions Fiat-Shamir heuristics alongside with El-Gamal. Does it have some sensible reasons? Could be the idea underlying El-Gamal signature be used for constructing proof-of-knowledge protocol? identification scheme? Could El-Gamal signature scheme be constructed from some proof-of-knowledge protocol by applying Fiat-Shamir heuristic?