down cold, have - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Learn or accomplish perfectly. For example, I have this song down cold. The slangy use of cold for “completely” dates from the late 1800s and the phrase itself from about 1900.