down cold, have
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.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.