Zero. The Cowboys are one only five NFL teams that have not officially retired a jersey number. The other teams are the Jaguars, Raiders, Ravens, and Texans.
If you suspected that the Cowboys had retired jersey #8 for Troy Aikman, #12 for Roger Staubach, or #74 for Bob Lilly, it’s true that no Cowboys player has won those particular jersey numbers in a regular season game since the retirement of Aikman, Staubach and Lilly, respectively.
Technically, however, those numbers are not retired. In fact, #74 has been issued to numerous linemen during training camp or preseason since Bob Lilly’s retirement following the 1974 season. However, no player has played in a regular season game wearing #74.