How do I get better at nutrition assessments for complex medical patients?

You can assess most patients well now, and that competence is real. What still trips you, the complex medical cases, are the ones that trip nearly everyone, because they stack conditions, medications, and interactions on top of plain nutrition. Struggling there is not a gap in your basics. It is the frontier of the skill. Those cases are hard because there is rarely one clean answer; there are competing needs that have to be weighed against each other. That weighing comes from seeing many of them, consulting when you are unsure, and slowly building the pattern sense that turns a tangle into a plan. No one shortcut exists. It is reps and reflection. So treat your hard cases as your curriculum. Keep a short log of the complex ones, what you decided, and how it turned out, and review it. Bring the genuinely murky ones to a colleague or specialist rather than carrying them alone. That habit is how the confusing cases slowly become the ones you are known for.