As a parent, I know how my child reacts when he is scared, tense or anxious. But I am not sure if I can relate the anxieties to exam stress because he is not open up a conversation with me.
Hi. I suggest you begin by noticing whether his anxiety occurs in different kinds of situations or is strongest at the time of exams. If he is anxious about other things too, it would mean that he has some fears which translate into anxious behaviours. If it is restricted to exams, then it would help for you to get him to talk about what goes on in his mind. Since he does not open a conversation with you, it would help for you to start sharing things with him - your interests, what your day was like, if you felt angry with someone, or happy about something. Have relaxed conversations about many things at the dining table. This gives him a sense of bonding, and comfort to gradually share his inner feelings with you.