Vague question. So I'll give general suggestions.
For Witness you can analysis each of the characters in terms of how belonging/isolation/lifestyle affects them.
i.e. John Book at the start: hard working cop, life revolves around his job.
What happens when he meets Rachael and her kid? He starts to grow some human compassion, etc.
When he's been excluded from the "cops" group, look at how he discovers a "new identity" with the Amish people.
The Amish don't really trust him either, what does that do to his sense of belonging?
You could also look at symbolism. Book's gun - violence, city life, his life as a cop ...
Barn raising - community/team work
The plain clothing the Amish wear
The bonnet Rachael wears. What does it symbolise when she takes it off?
Look at Holden in Catcher and his views on "phonies" etc. Where does he even belong? You can look at the people he encounters and how their relationship/lack of relationship affects him and his outlook on the world.
You just need to refer to those texts in relation to a prompt, draw out examples and make sure everything's relevant.