when to take a cutting and how to try to get the cutting to root

I would be inclined to take a heel cutting for this, anytime from now until autumn. Choose a young unflowered sidestem and peel it away carefully from the main stem so that you have a good 'heel' on the piece you wish to propagate.
Remove all but the top two pairs of leaves and trim the heel so that there are no tiny slivers of green bark that could rot and ruin your cutting. Dip the heel in rooting hormone ( I prefer liquid, it has less tendency to clump ) then insert the cutting/s round the edge of a pot filled with moist, multipurpose or cutting compost. Place in a coldframe or sheltered spot, and mist spray daily until the cutting/s show signs of new growth.

You could try layering some of the lower branches by cutting a slanting cut, wedge it open with a piece of grit. Bury it into the ground about 2 inches, peg it down, keep the ground around your Ceanothus Skylark damp at all times, by early spring you will have a large shrub or two to plant out.