How can I find out what the current Segregated witness adoption rate is, so as to see how it is progressing towards the 95% readiness required for it to activate.
There is nothing to track until 0.12.2 is released. Once that happens the process is described here:
"First, miners (or pools) running Bitcoin Core 0.12.2 (and Bitcoin implementations that merged similar code), automatically start signalling they are ready to mine Segregated Witness transactions. This happens through version bits they include in blocks they do mine that indicate what types of transactions and blocks they can mine.
Once miners representing 95 percent of hash power (1,916 blocks) within a single difficulty period (2,016 blocks/about two weeks) include the right version bit, the soft fork is locked in."
Block explorers will make it easy to track the progress after 0.12.2 is released
Bitcoin Core has a segwit adoption page that should help you track it: https://bitcoincore.org/en/segwit_adoption/