Answer:
Some
Step-by-step explanation:
In the sentence above, the adjective of quantity is "Some". An adjective describes a noun or a pronoun in a sentence, giving us ideas about its size, color, state, quantity, quality, beauty, etc. The noun, Juice in the sentence, is qualified by the adjective, 'Some', to indicate an item of unspecified quantity.
The character mentioned that he/she had Juice for breakfast but the exact quantity of juice the individual consumed was not mentioned. Therefore, some is the adjective of quantity.