Is "sinecure" used correctly in this sentence:
He studied hard throughout college to get a sinecure job.
I doubt if you mean that sentence. Study this definition and see if that's really what you mean.
http://www.merriam-webster.com/dictionary/sinecure
sincere
No, the word "sinecure" is not used correctly in that sentence. A sinecure refers to a job or position that requires little or no work, yet provides a salary or financial benefits. It typically implies a position of privilege or an easy job obtained through connections or nepotism.
The sentence suggests that the person studied hard in order to obtain a sinecure job, which contradicts the concept of a sinecure. In this context, it would be more appropriate to use a different term, such as a prestigious job, a well-paying job, or a job with excellent benefits.