how much; how many; to what extent
Used to ask about quantity, degree, or extent. Can also be used in exclamatory or rhetorical expressions.
How long do I have to wait?
No matter how much I practice, I can't get better.
I don't know how many people will come.
どれだけ and どんなに can both mean 'to what extent', but どれだけ often has a quantitative nuance (how much/how many) while どんなに emphasizes emotional degree.
Compound of どれ (interrogative pronoun) + だけ (extent/amount). The kanji spelling 何れ丈 is ateji and rarely used.