What we today call the "two great commandments" were well-known in Jesus' day
Both commandments had been previously given by Jehovah.
1st Great Commandment: And thou shalt love the Lord thy God with all thine heart, and with all thy soul, and with all thy might. (KJV Deut. 6:5)
2nd Great Commandment: Thou shalt not avenge, nor bear any grudge against the children of thy people, but thou shalt love thy neighbour as thyself: I am the Lord. (KJV Lev. 19:18)
So it depends on what you mean by "shared."
- Jehovah was the first to express the ideas.
- Moses was the first to write the ideas down.
- Whomever taught the lawyers of the New Testament the doctrine were before Jesus or the lawyers.
As I led off, the two great commandments were well-known doctrines of the day. They were not introduced first by either Jesus or the lawyers in the New Testament, but were introduced by Moses via Jehovah in the Old Testament and would have been regularly studied in the rabbinical schools. I believe it is reasonable to assume that both the lawyers and Jesus learned the two commandments as children.
… Which is why Jesus' response to the lawyer in Luke 10:26 makes perfect sense.
However, if what you're asking is, "but in that specific situation (or situations), who introduced the idea first, the lawyers or Jesus?" that I can't help you with. I hope I was a spiritual observer, but that veil has been drawn and I doubt there's enough historical evidence to be definitive.