The show command either gives information on the indicated unit types. This information is gleaned directly from the current Empire data structures so is always up to date. The format of each output is more fully described in the relevant info pages (Ship-types, Nuke-types etc.).
Unless the unit is a bridge, a further parameter is needed to indicate
whether you wish information about construction of units, the statistics
of units or the capabilities & abilities of units.
So, for example
[##:##] show nuke capabilities
will give something like
blst dam lbs tech $ 10kt fission 3 80 4 200 $7500 50kt fission 3 100 6 225 $9000 100kt fission 4 120 8 250 $12000 250kt fusion 4 150 4 280 $7500 500kt fusion 5 170 6 295 $9000 1mt fusion 6 190 8 310 $12000 3mt fusion 7 210 10 325 $19000
Note that you can only get information on items that you are actually technologically capable of building (within 1.25 times of your current tech.)