What is the last step in the synthesis of secretory protein synthesis? I think it is exocytosis but the other choices I have are tagging, endocytosis and osmosis.
http://en.wikipedia.org/wiki/Exocytosis
You are correct, the last step in the synthesis of secretory proteins is exocytosis. Exocytosis is a cellular process by which the secretory vesicles containing the newly synthesized proteins fuse with the plasma membrane, releasing the proteins outside the cell.
To find this answer, you can refer to reliable sources such as textbooks or scientific articles on cell biology or protein synthesis. In this case, Wikipedia is also a useful resource. By searching for "secretory protein synthesis" on Wikipedia, you can find the information under the section on exocytosis. Reading through the relevant section will provide you with a clear understanding of the last step in the synthesis of secretory proteins.