I understand that a L2 device like WAP is needed to forward packets
from one client to another within the same network (based on MAC
mostly like in 802.11)
Only in Infrastructure Mode.
However my question is, if there is no WAP and just a wifi router
available(L3 device) to which clients are connected..then.. is it
really possible for clients to be able to talk to each othet?
What you call a "wifi router" is a combination of a WAP and a router, and they are completely separate functions in different devices that are connected internally in the same physical box. Some router models can also have a switch module, but the routing and switching are also separate functions on different devices in the same box.