Threatened by the javelin of his own father, Jonathan was finally convinced that Saul meant to slay David is True.
Step-by-step explanation:
Jonathan gave David his own regal pieces of clothing, his sword, and his bow, consequently intrigued to know about the peril that may undermine his dad or the realm. Also, Jonathan addressed Saul his dad, and said unto him, Wherefore will he be killed and hath a spear at him to destroy him: whereby Jonathan realized that it was resolved of his dad to kill David.
At the end of the day, Saul isn't compromised by David; he is undermined by any individual who may assume a job in the assignment of his substitution. So Threatened by the javelin of his own father, Jonathan was finally convinced that Saul meant to slay David is True.