Let me question your question briefly, then reassure you, then try to answer it. Precious few experts in philosophy lack what they and other people would consider serious gaps. Many, many philosophy professors are not all that familiar with material that's taught by others even in fairly introductory-level courses. This is far from unique to Philosophy. You will find it is the case in most academic fields.
You might think of philosophy as primarily as a style of approaching problems, together with a very broad literature that approach has generated, together with the continued study and curation of parts of that history. Experts in philosophy are recognizable to others far more because of their style of reasoning, discussing, and attacking problems than for their lack of gaps.
In part, this is meant to reassure you: don't worry about gaps! Focus on topics, problems, and figures who interest you, and expand out from there.
That said, your question about undergraduate curricula is a good one. I don't know where to find a full curriculum because it would have to include all the individual professors' syllabi, and those are rarely all placed together online by departments. One interesting, though fairly narrow, reading list is here, at Cambridge University, for undergraduates and graduates.
Most undergraduate philosophy departments probably offer a set of courses which will include the following:
- Introduction (simply some subset of what's below, based on instructor preference)
- Informal Logic or Critical Reasoning
- Symbolic Logic
- Ancient Philosophy (Presocratics, Plato, Aristotle, and perhaps Stoics, Epicureans, Skeptics)
- Medieval Philosophy
- Modern Philosopy (Descartes, Bacon, Locke, Hume, Berkeley, Leibniz, Spinoza)
- 19th Century Philosophy (Kant, Hegel, Kantians, Hegelians, Marx, Sidgwick, Mill)
- Existentialism and Phenomenology
- Ethics (generally both normative ethics and metaethics, Kantianism, Utilitarianism, and Virtue Ethics)
- Applied Ethics (a set of contemporary moral problems)
- Political Philosophy, or Social & Political
- Philosophy of Mind
- Philosophy of Science
- Philosophy of Language
- Philosophy of Art / Aesthetics
- Philosophy of Religion
- Eastern Philosophy
Beyond that core set which one finds in most departments, course-offerings vary radically, and may include such offerings as Feminist Philosophy, Biomedical Ethics, African Philosophy, 20th Century French Philosophy, Philosophy of Law, and many others.
In trying to get a sense of what's out there, I would consider looking at the Stanford Encyclopedia of Philosophy entries for some of these areas that interest you. Though those articles can get technical, they have a lot of good references and links out. If you're not sure what you might want to look at first, and you want a sense of what a professor might say and have you read in an excellent Introduction to Philosophy course, take a look at Simon Blackburn's book Think.