Wash inside out in cold water to preserve color. Wash separately for the first few washes — denim may bleed. Do not bleach. Line dry. Avoid high heat, which can affect the fagoted shard panels and button finish.
Double knees are a workwear convention — a second layer of fabric over the knee, there to take the wear the rest of the garment doesn't. Here that second layer is built from fabric shards, fagoted on rather than simply patched.