Typically, network analysis capture files such as .snoop files from Solaris are converted to similar formats so they can be analyzed in a different software, which means export to .txt file is not a common thing. It is also not useful to open .snoop files in a text editor.
It looks like you can achieve this by using the "snoop detail" command and specify the desired file the data will be saved in, which essentially achieves snoop to txt conversion.
Some 3rd party protocol analysis programs like Wireshark may be of help as well.