Now that we have the Code of Canon Law, and the 1917 version is on prepub, some choices that would be immensely helpful:
1. Heinrich Denzinger, Compendium of Creeds, Definitions, and Declarations on Matters of Faith and Morals. This is the "go to" book in seminary for researching church teaching.
Please be sure to use the latest edition, the 43rd printing! The forward says this is first English Denzinger since 1957, the 30th ed., over a a half century ago. This edition is an exact translation of the 43rd German edition, which added material from the pontificate of Pope Benedict XVI up through 2008, which means Summorum Pontificum par. 1, and the introductory letter.
2. A series of excellent reference books on Canon Law, the most important being the best book IMHO on Commentary about Canon Law, The Pastoral Companion, 4th Edition (do not get older editions!) by Dr. John Huels.
3. Another excellent Canon Law Commentary, New Commentary on the Code of Canon Law