There are two different ways to achieve this:
1. If you know the rank of the user: In this case, you can call getTopNRankers API where you can play with offset and max parameters to get the users around any particular rank. For example, if the rank of a user is X and you want to know users aroud this rank say 5 with lower rank and 5 with higher rank. You just have to set offset as X-5 and Max as X+5.
2. If you know the score of the user: You know the score of the user, you can decide the score range in which you want to know the users and call getUsersWithScoreRange API.
Please let me know if you have any further query, I will be happy to help you.