There is a small airport near Tobolsk, but commercial flights are availalbe to Tyumen.
Flights to Tyumen are available on a number of airlines to Roschino Airport.
We tried SkyExpress airlines.
Be aware some potentila problems. Sky Exprtess blies nice Boeing 7377-500 jets.
But they may cancel flights without warning. Our was cancelled, we got a next day flight.
We were promised a window seat by the smug Sky Express agent.
Be warned-- seat 7f is not a window seat! Row 7 does not have a window!
The major trans-Siberian trains go through Tyumen, not far from Tobolsk.
Trains from Moscow (or St. Petersburg via Moscow) are not difficult.
Then at Tyumen you can catch a local train or bus to Tobolsk.
(Tobolsk was the major siberian city before the main train bypassed it)