The pronoun "you" is the subject in the sentence "Do you know the origin and customs of Kwanzaa?"

Specifically, the subject directs the action of the verb "know." The direct objects are "the origin and customs." They are the recipients of the action of the verb in a sentence.

Maulana Karengacreated Kwanzaa in 1966 as the first specifically African-American holiday.Karenga said his goal was to "give Blacks an alternative to the existing holiday and give Blacks an opportunity to celebrate themselves and their history, rather than simply imitate the practice of the dominant society."
During the early years of Kwanzaa, Karenga said that it was meant to be an alternative toChristmas, thatJesuswas psychotic, and thatChristianitywas "a white religion which black people should shun".As Kwanzaa became more popular, Karenga modified his stand to avoid alienating African-American Christians. In 1997 he backtracked on his original statements and declared:
"Kwanzaa was not created to give people an alternative to their own religion or religious holiday."

Most African-Americans who celebrate Kwanzaa do so as a celebration of their heritage and the 7 principles that it espouses so that is now the real purpose of Kwanzaa. It is very common for those celebrating Kwanzaa to also celebrate Christmas.

It's no different than any other type of card:

• Salutation: Dear xxxx
  
• Closing: "Love, xxx" or "sincerely, xxxx"
  

Also, note that giving cards on Hanukkah is not traditional. It is something that only some Jews do, which is borrowed from Christmas.

Here's something right from Wikipedia:

Karenga created the organization US, a Black Nationalist group, in 1965. He later became chairman of the black studies department at California State University, Long Beach, a position he held from 1989 to 2002. [1] He is also known for having co-hosted, in 1984, a conference that gave rise to the Association for the Study of Classical African Civilizations, and in 1995, he sat on the organizing committee and authored the mission statement of the Million Man March. He is the director of the Kawaida Institute for Pan African Studies[2] and the author of several books, including his Introduction to Black Studies, a comprehensive black/African studies textbook now in its third edition.