Topping bread with poppy seeds or sesame seeds Should the seeds be sprinkled over the dough before baking, or will they burn?

Should they be soaked first to prevent burning?

Should a wash (cornstarch?) be used to stick them to the dough?

Anything else I need to know?
You should sprinkle them onto the dough before baking. They shouldn't burn, but they will toast and release some tasty oils. You don't need to soak them either.

Using a wash depends on the wetness of your dough. If it's fairly wet, you'll probably be fine. If it's a drier, more stable dough, use a simple egg wash, which will help the seeds stick and give a nice glossy finish to the top of your loaf.