Suppose I have:
Clients -------- switch-------router--------router----------router (netflow enabled) ---------switch---------Servers
In the above topology netflow only enabled in the last cisco router. Will i still be able to monitor which clients are using up bandwidth to the Servers? Or should I enable netflow on the first router?
Yes. In the example you provided above, enabling NetFlow, sFlow, JFlow, or IPFIX on any device between the client and the servers would provide you with the information you're looking for.