Hi Sijo,
If I understand your requirement correctly, you have a field in a form view(not table view field. Right?). And you need this field having a tooltip for both label and input fields. I will check whether get_p works for label or not on Monday as I don't have the system access now. However, can you check the type of cl_thtmlb_label is coming so only in display mode?. I mean, whether it comes properly in edit mode or not.
You can have a look in this discussion How to add a tooltip to a TableView header Column also.
Thanks,
Faisal