You can have a look through all of Satoshi's writings here:
https://satoshi.nakamotoinstitute.org/And you can also have a look through all of his forum posts here:
https://bitcointalk.org/index.php?action=profile;u=3As far as I can tell, he never directly mentioned taxation. Tax is mentioned briefly in a couple of the early email chains between Satoshi and people like Hal Finney and Ray Dillinger. I'll paste the relevant sections here:
I know the same (lack of intrinsic value) can be said of fiat currencies, but an artificial demand for fiat currencies is created by (among other things) taxation and legal-tender laws. Also, even a fiat currency can be an inflation hedge against another fiat currency's higher rate of inflation. But in the case of bitcoins the inflation rate of 35% is almost guaranteed by the technology, there are no supporting mechanisms for taxation, and no legal-tender laws. People will not hold assets in this highly-inflationary currency if they can help it.
In the modern world, no major government wants to allow untracable international financial transactions above some fairly modest size thresholds. (The usual catch-phrases are things like "laundering drug money", "tax evasion", and/or "financing terrorist groups".) To this end, electronic financial transactions are currently monitored by various governments & their agencies, and any but the smallest of transactions now come with various ID requirements for the humans on each end.