Family Lore Clinic 1: Can I take my son to court to see my grandchild?
I assume that the situation that the poser of this question finds themself in is that their grandchild lives with their son, who is refusing to allow them to have contact with the grandchild.
The answer to the question is yes, you can take your son (and the child's mother) to court to seek a contact order, although you will first need the permission of the court to make the application.
For further details regarding applications for contact by grandparents, see this post.
If you require specfic advice, then you should consult a specialist family lawyer.