My concern is that - Why is your concern? Are you HR/Owner?
How to ask to mark attendance from - Do you have any prevailing system of attendance?
The Senior consultant of the Company. - What is meant by this? Are they Owners? Appointed specially by owners?
After so many reminders, he is not marking their attendance. - How have you reminded him? Have you ever kept your reporting authority in the loop while doing this? If yes, what is the response of your reporting authority? If no, then involve him/her now.
Please suggest what should I do in this situation? - Share the above-asked information to suggest better.