I am NOT 100% sure, but I think it's the following:
Traffic is sent from 10.10.1.7 to 10.20.1.6
Subnet Mask of both IP Addresses is NOT given, but because the question says that RIPv2 is Enabled, you can assume that both IP Addresses are NOT on the same network.
Because 10.10.1.7 and 10.20.1.6 are NOT on the same network, you need a Router to pass the traffic from the PC to the File Server.
So that's why the traffic goes from Switch1 to Router1.
The question says that RIPv2 is Enabled on ALL Layer 3 Devices. All Routers are Layer 3 devices.
So Router1 and Router2 has RIPv2 Enabled. Because of this, they can and will establish an adjacency with each other, assuming RIPv2 is configured correctly.
The traffic will then go from Router1 to Router2.
And then Router2 will forward the traffic to Switch2 and Switch2 will forward the traffic to the File Server.