Good luck on Monday! Here's roughly what adult assessments cover, so you can jot down examples without rehearsing answers (I'm on a medical editorial team that writes about ADHD, so general info only, clinics differ a bit):

• Childhood. Symptoms need to have been there before about age 12, so expect questions about school: reports like "could do better if they tried", losing things, daydreaming, unfinished homework, trouble for talking or fidgeting. Old school reports or a parent's memories help a lot.
• How it shows up now, in different places. Work or study, home, money, relationships. Concrete examples work best: late bills, abandoned projects, lost keys, missed appointments, interrupting, hyperfocus on some things and paralysis on others.
• Impact. Not just what you do, but what it has cost you: jobs, deadlines, fines, conflicts.
• Other explanations. Sleep, anxiety, mood, substances, thyroid. Answer honestly, it doesn't count against you.
• Questionnaires. Often the ASRS, sometimes one for a partner or parent too.

Practical trick: a one-page list of real examples on your phone, sorted childhood / work / home, and tell them at the start that you blank in the moment and made notes. Clinicians are used to that, honestly it's pretty on-brand for the assessment :)