If you’re just running the CoreNLP pipeline, please cite this CoreNLP demo paper. If you’re dealing in depth with particular annotators, you’re also very welcome to cite the papers that cover individual components (software pages).

Manning, Christopher D., Surdeanu, Mihai, Bauer, John, Finkel, Jenny, Bethard, Steven J., and McClosky, David. 2014. The Stanford CoreNLP Natural Language Processing Toolkit In Proceedings of 52nd Annual Meeting of the Association for Computational Linguistics: System Demonstrations, pp. 55-60.[pdf][bib]