Studies /ˈstʌdiz/. From study + -es: the y changes to i before the ending, so the spelling becomes studies.
She studies every evening.
Where you'll see it
My studies take most of my time this term. Here studies is a plural noun meaning the work you do at a college or university.
Her studies include history and French. Here studies is also a plural noun for the work you do at a college or university.
One sound to watch
The stress sits on the first syllable only: /ˈstʌdiz/. Say STUD-eez. The -ies spelling is not pronounced as two syllables; it sounds as one, /iz/, with the vowel /ɪ/. Trust the /ˈstʌ/ beat and the rest follows naturally.
Watch the spelling trap around that /iz/ ending. Because the sound is /z/ not /s/, the common slips go in two directions: some learners leave the y alone and write studys, while others double a letter and write studdies. Neither doubled letters nor dropped letters are needed. Study swaps y for i and adds es, in that exact order, giving studies. That spelling is the only accepted one in both British and American usage.