I was watching the system design playlist and while it's good it feels like it's frontend oriented. My question here is that let's say that we get a big epic to work on, where we have to do something similar of what is already implemented in the application, but this time we have to do something else on that similar line. The main point I want to emphasize is that we normally have screenshots from the product design side and we have to come up with models and apis and everything else(considering there are more than 10 apis to build).
What is the best way to proceed in such situations?
I'm a bit confused as to the problem here: Is the idea that because this epic is based of an existing feature, it's missing some resources like screenshots and that ambiguity is holding you back?
I'm unsure how fitting this advice is without knowing your level, but in a vacuum, I would just suggest that you fill in the gaps yourself. The best engineers I've worked with weren't afraid to hybridize behaviors and go outside of the pure technical scope to move a project forward. For example, here's what you can do with the missing screenshots from the product design side issue:
In terms of everything else, it seems like you're in a decent starting point as there's an existing model to follow in your application. When in doubt, go for consistency. Mirror whatever design patterns the existing use case has - More or less just copy-paste everything and swap out values to fit your scenario. I've been surprised at how often this gets messed up: A sadly common example is that the data model between 2 features has similar fields but the keys are named differently.
Lastly, I recommend this discussion on how to get better at technical design overall.
Given a big feature to work on what is the best way to proceed?
Just decompose the problem and get consensus about:
I don't understand from your question what is different in your scenario.