hello,I skinned parts just like the video of easycomposites,it is better to post cure one time at the end of the project or I must post cure the first layer of epoxy which is applied to do the trimming?

You are best to post cure after the last layer of resin has been applied and cured, but NOT sanded smooth.  You would likely get some movement and sinking of the resin during a post cure, so it is best done before the final sanding smooth.  Once postcured, you can sand smooth and polish back to a gloss as normal.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant