First this episode in Mark's Gospel and then it is important to compare it with Matthew's account (Mt 22,34-44): consider how Mark differs from Matthew and what is special about his version?
Then have a look at this incident in Luke's Gospel (Lk 10,25-37). What is special there?
How does the scribe approach Jesus in verse 28? Note how the scene is set very differently to the preceeding encounters.
For the first commandment quoted by Jesus see Dt 6,4-5. Look at Levitcus 19,13-18 for the second commandment. These OT passages form Jesus' reply to the scribe, 12,29-31.
The scribe in his reply, 12,32-33, then takes Jesus a step further. Look at Dt 4,32-36 (note that I have added some context to the various quotations in this passage.)
For the second part of the scribe's reply, look at 1 Samuel 15,22 & Hosea 6,6.
What do you make of Jesus' comment in verse 34?
Time now for my response.
This encounter with the scribe, Mk 12,28-34, forms the Gospel for the 31st Sunday in Ordinary Time.
The Sunday Lectionary leaves out all of chapter 11 and much of chapter 12 between the 30th and 31st Sundays. It goes straight from Bartimaeus (10,46-42) to the scribe. As we come to this reading for the 31st Sunday therefore, we need to keep in mind all that has happened in between, especially that this Gospel follows the series of controversies between Jesus and the various Jewish groups.The Old Testament reading chosen to accompany the Gospel is the passage quoted by Jesus, Dt 6,2-6. Read the whole passage in the Book of Deuteronomy (Deut 6,2-9). The second part of the reading is the opening of the prayer which is recited by Jews not only in the time of Jesus but also up to our own days: Shema Israel, "Hear O Israel".
We can now continue to the remainder of the chapter, from 12,35 through to 13,2.