what is better to say " to feel resentful or feel resentfulness"? have no clue

Question

Answer

В этом случае правильный вариант "to feel resentful".
После следующих глаголов "sound, feel, taste, smell" должно употребляться прилагательное.

Answer

That really depends on what you want to say.

1. He feels resentful towards something or somebody.
2. He feels a lot of resentment in his life.

"Resentfulness" is a very abstract noun, and is usually preferred by Russians and Germans.