Hi @bp_sin,
Have you tried starting up a mongod instance with your backup copy of this dbPath as mentioned earlier?
mongod --dbpath /path/to/your/backup
If mongod is able to start successfully, you can query and export data using standard tools like the mongo shell and mongodump. Assuming the data you are looking for is present, try to follow the general guide I suggested earlier in this discussion.
If mongod has any issues reading the data files, there should be warnings logged on startup with more context on files that are missing or problematic. If you don’t have a viable backup copy, your options are limited and unlikely to be fully successful (see Recover corrupted files (MongoDB 3.0.12) .wt - #4 by Stennie, which Chris mentioned earlier).
The specific steps involved require an understanding of the data you are trying to recover and ideally someone who is working through the process with you directly (i.e. a MongoDB expert from your DBA team or an external consultant).
Regards,
Stennie