Jack asks questions about Nath to understand their relationship. Lydia initially likes the locket but later despises it. Lydia fails her driving test and Hannah notices a change in her at her birthday dinner.
Jack asks many questions about Nath during his drives with Lydia because he is interested in learning more about Nath and wants to understand Lydia's relationship with him. The questions help Jack gather information and gain insight into their past and dynamics. Lydia initially likes the locket her father gives her because it is a sentimental gift, but she later comes to despise it when she learns the truth behind its origins, which represents betrayal and deception.
Lydia fails her driving test because she is distracted by her thoughts and emotions, which impact her ability to focus and make proper driving decisions. Only Hannah notices the change in her at her birthday dinner because she is observant and in-tune with Lydia's behavior. The change that Hannah notices could be a change in Lydia's mood, attitude, or demeanor.