Can we view the packet content in NS2? – (not the header)

By default, an ns-2 packet will not contain any payload. Payload is just mentioned as size in the packet header. So, under ns-2, generally, there will not be any payload data.

So, you can not print that nothing.

For advanced Users :

The message passing agent of ns2 will hold little bit of sting data along with the packet – learn to use message passing agent

There exists another way to send real payload under ns-2 – but as far as I know, no one ever used that in any of the research simulation. (Some earlier video trace related projects used real payload under ns-2? – I am not sure)