How can I measure the amount of carbon dioxide emmissions when wood is burned?

Assuming that the wood contains only carbon, water and oxygen, you could burn the wood in a known excess of oxygen, pass the gas produced in water to remove all the water, then pass the resultant gas though lime water and collect the residual gas which is oxygen only.

From that, you can get the amount of oxygen used for combustion, and deduce the amount of carbon dioxide produced.

If you dry the gasses and then pass them through a soda lime or Ascarite tube you can weigh the absorbed CO2 directly.