Is Shobi's father that Nahash?
There is an eye-gouging King Nahash (1 Samuel 11:1-3) whom King Saul defeated and earned the eternal loyalty of Jabesh-gilead (1 Samuel 31). There is also a King Nahash who dealt loyally with King David (2 Samuel 10:2). These are probably the same person, but who knows? Josephus claims the Nahash of Saul's reign died during the battle in 1 Samuel 11. (Antiquities of the Jews - Book VI: Containing the Interval of 32 Years. [From the Death of Eli, to the death of Saul.] by Josephus, Volume 6, Chapter 5, Section 3 @ https://penelope.uchicago.edu/josephus/ant-6.html, accessed June 9, 2023)
Rabbah seems to be the Ammonite capital, since Joab sieged it (2 Samuel 11:1) and David took the crown off the king's head there (2 Samuel 12:2-29). Also, the city is a capital today, though now it is Amman, capital of Jordan. (https://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/rabbath-ammon) Kings usually live in the capital city. So even though the Bible never says King Nahash lived in Rabbah, they probably did, right?
If King Nahash was loyal to King David, perhaps his family, excluding Hanun (2 Samuel 10:6-19), is still supporting him after his death in 2 Samuel 10:1?
Maybe David earned the loyalty of yet another Nahash in Rabbah, and that guy is Shobi's father. David took all the cities of the Ammonites, starting with Rabbah, and made them serve Israel (2 Samuel 12:2-29), so idk if this would be David having so much charisma that he makes friends everywhere or sycophancy à la Ziba (2 Samuel 16:1-4) or if living in a vassal city of Israel is better than living in the capital of the Ammonites or what.
As a side-note, there also seems to be a Nahash in David's family. David and Abigail are brother and sister, but the Bible isn't explicit in whether they share the same parents. 2 Samuel 17:25 says Abigail is the daughter of Nahash. I've seen explanations that the name is part of a corrupted text, Nahash is another name for Jesse, Nahash is Jesse's wife, and that Jesse married a former wife or concubine of the actual King Nahash. In other words, no one knows.
David's mother was a maidservant of the LORD (Psalms 116:16), so poor girl if she came from Ammon. If that's the case, she reminds me of Abigail of Carmel, especially given the similarity of the names and proximity to David. This Abigail waited on the LORD until she was delivered from her harsh husband Nabal. David took her as a wife soon afterward. (1 Samuel 25)
Biblical Account
King David receives a gift of supplies and food from Shobi in Mahanaim while preparing for Absalom to attack and try to take his throne by force
King David fled Absalom and all Israel who were seeking to kill him and take his thone. David crossed the Jordan and came to Mahanaim. Absalom crossed the Jordan with all the men of Israel. When David came to Mahanaim, Shobi the son of Nahash from Rabbah of the Ammonites, Machir the son of Ammiel from Lo-debar, and Barzillai the Gileadite from Rogelim brought beds, basics, earthen vessels, wheat, barley, flour, parched grain, beans, lentils, honey, curds, sheep, and cheese for David's hungry, weary, and thirsty men.