What is the interpretation of seeing a person in a dream asking the dreamer to marry a specific woman, knowing that the dreamer is married and happy in his marriage?

A dream does not necessitate anything. If there is no legal impediment, the default is that marriage is permissible, based on the Almighty's saying: "Marry such women as seem good to you, two, or three, or four." Care should be taken to maintain harmony with the current wife. If a second marriage does not lead to family dispersion, and you are able to fulfill marital rights and act justly, then marriage is good because it increases progeny and provides chastity for Muslim women.