Looks to be good structure and the places you have marked are places to start I always like to check drop offs and deep water adjacent to them shallow flats in low light times close to deep water and average depth humps. But if you can't find them just start cutting holes and search with a jigging spoon tipped with a minnow and your electronics if nothing comes in after 3-5 min move on. This technique works well for me hope it does for you too. I never stay in the same place in the summer if not catching fish why would you in the winter.