If you look at the entry for work in the Cambridge Dictionary,you will see that there are entries for both countable (marked with a C) and uncountable (marked with a U) definitions.
A countable noun can have a plural, for example book/books. an uncountable noun does not normally have a plural, for example sugar
As an uncountable noun, work can have this meaning: the material used by someone at work, or what they produce
As a countable noun, work can have this meaning: something created as a result of effort, especially a painting, book, or piece of music
If, for example, you are talking about an author, both of the sentences that you have proposed are acceptable. If you choose to think of the author's work as one collective item, you would use the uncountable form, so sentence 1 is correct. If you choose to treat each book that the author has written as a separate item, then sentence 2 is correct.