Deployments used to emit coverage data, but that changed in some recent-ish version.
To get coverage/failed test information now, you need to add the --verbose flag
If you're using the --json flag to output results as JSON, the coverage information is contained in result -> details -> runTestResult -> codeCoverage. The "numLocations" gives you the total number of coverable lines for a class, and the "numLocationsNotCovered" gives you the number of lines not covered.
You'll need to calculate the percentage yourself (1 - uncovered/total)