There is a smoking room in the international departures area. I think there's one near the food court area. There will be signs all around for sure.

The lounge situation in DEL is awful. If you're *G you get the completely uninspiring AI lounge. Encalm lounge is entry through credit cards & PP... I don't know if they have a paid entry. If you can't enter Encalm you still have plenty of relaxing areas, food courts etc. around the departures area. Although spending 6 hours there won't be fun.