睦 rarely stands alone in modern Chinese - you'll almost always see it in compounds like 和睦 (harmonious), 睦邻 (good-neighborly), or 亲睦 (close and friendly). Learn it through these pairings.
目 on the left is the eye radical, a vertical pictograph of an eye. It tags 睦 as a looking-related word; harmonious eyes that meet without flinching mark the friendly gaze 睦 names. Compare 看 (watch) and 眼 (eye).
坴 supplies a phonetic that has drifted from lù to mù, the two sharing closely related Old-Chinese onsets. The same phonetic appears in 陆 (land) and the original 睦 keeps the warm-earth flavor of solid ground that people stand on together.
