Sharing our experience as DS recently did his 11+ exams in Bucks and Berks - Comprehension was the biggest issue with my DS last year. But over the time, working together helped DS overcome his weakness in it to some extent. I wouldn't say he is excellent in comprehension now but much much better than he used to be at the beginning of Yr5. We read together many classical books (with learning new words and asking questions) and worked on various comprehension test books - CGP, Letts, FPTP, Schofield & Sims and a little of Bond books. We started with easier ones first (9-10 age group) to build his confidence then progressed to 10-11 ones. We also referred to Bond - How to do 11+ English book to learn various techniques. All this, not only helped him to do well in his 11+ exams and in his school exams (which made him move to set 1), but also helped me to improve my English skills

, as it's my second language.
There isn't any concrete strategy to master in comprehension as every child is different. So, work together and have faith, is the only suggestion from me!
You can also refer to other threads on this forum which already provide valuable advice/tips to address this issue.
Good luck!