Is this a typo, or can you get the mass with just molar mass and molarity?

It's not so much a typo, as an omission.

The volume of the 0.3M solution has been omitted. To find the mass of the solute we would need to know the volume of the 0.3M solution.

For instance, "How many grams of NaCl are needed to prepare 500 mL of a 0.3 M stock solution?"

0.5L x (0.3 mol NaCl / 1L) x (58.5g NaCl / 1 mol NaCl) = 9g NaCl

"How many grams of NaCl are needed to prepare a 0.3 M stock solution?"

This is a typo.
Molarity = (Mass of NaCl) / (Volume of solution)
Hence, Mass of NaCl = Molarity × (Volume of solution)

Mass of NaCl is found by both the molarity and the volume of the solution. Now, the volume of the solution is missed, and thus the mass of NaCl cannot be found.

No, you can't.
You need to know some other quantity to complete the calculation - volume of solution, mass of solution, mass or volume of solvent - something.

It's a good idea bc if you make broth then you can water down what you already have instead of always making a fresh batch when you need it