。
I feel like there's something missing from my life.
Literal
I [of-の] life [in-には] something lacking-is thing [subject-が] exist [seem-ような] feeling [subject-が] do [explanatory-んだ].
A beautifully complex sentence-final construction: ~ような気がする ('to feel as if, to have a feeling that'). 何か ('something') introduces an indefinite subject. 欠けているもの ('a thing that is lacking') uses ~ているもの to create a relative clause. The whole structure nests: '[clause] [exists] [such that it feels]' — introspection and tentative assertion layered together.