Where did the high priest sprinkle the bullock's blood on the Day of Atonement?
The high priest took the bullock's blood behind the veil and sprinkled it upon the mercy seat—the beautiful, golden mercy seat of the cherub—as the sacrifice for himself and his family. This occurred once a year on the Day of Atonement, before he cast lots upon the two goats.
Les explains that the high priest first came all the way through the sanctuary and then, once a year, passed behind the veil. There he sprinkled the blood of his sacrificial animal, the bullock, upon the mercy seat. This bullock was used for his own sacrifice, himself and his family. After that, he came to the two goats and cast lots to determine which goat would be killed and which would be left alive as the scapegoat. The goat chosen by lot to be put to death had its blood taken through the same process, and he again came behind the veil and sprinkled it upon the beautiful, golden mercy seat of the cherub. Les notes that some people imagine the mercy seat was filthy with dried blood, but the priests did not sprinkle gobs of blood. They dipped a finger in the basin and just touched it, so there were no gobs of blood upon the gold. He simply used his finger to present the blood.
And he shall take of the blood of the bullock, and sprinkle it with his finger upon the mercy seat eastward; and before the mercy seat shall he sprinkle of the blood with his finger seven times.