Is a son's demand for his right and his filing a complaint against his father and the buyer to obtain compensation for his efforts in mediating the sale of a plot of land considered disobedience to parents (ʿUqūq al-Wālidayn)?

The father's right to dutifulness and respect is established and is not contingent on his treatment of his child. If you had agreed with your father on a known wage for your effort in selling the land, and the sale was completed, then this wage is confirmed as a debt owed to you by him. Scholars have differed on the child's right to demand a debt from his father. The Hanbalis do not permit this, while the majority of scholars believe the child has the right to demand it and take the matter to court. It is preferable not to complain about your father or take him to court, as an act of kindness towards him. You must be dutiful and respectful to him, whether you demand the debt or forgive it, for the father's right is great and is not forfeited by his injustice towards his child.