Can I use regular sugar instead of powdered sugar to make a drizzle icing for my pound cake?
It depends on the type of recipe you want to use, but generally the answer is yes. Powdered/confectioner's sugar recipes for glaze or icing often just use a very small amount of liquid. With granulated sugar, it can be difficult to get a smooth consistency by just adding the liquid that way, so the more standard way with regular sugar is to add a small amount of water to a pan and cook the sugar in it until it dissolves and creates a thick syrup.
(Alternatively, if you just don't have confectioner's sugar on hand, you can grind up granulated sugar in a blender or coffee grinder. Some also recommend food processors, but many of them won't get a consistent fine grain in your sugar. Just pulse until particles are fairly small and the sugar is powdery. The particles may then be small enough to dissolve quickly in your icing recipe.)
If you have some cornstarch and a coffee grinder on hand you could also make powdered sugar.