Apply the mesh as you did throughout the rest of the column. Just spread a thin layer of mortar over the top course, put down the mesh, and top it with another thin layer of mortar. Don't skip this step. You'll need the wire mesh to help support the final course of bricks, which will have an extra brick in it. Since this will be the top of your brick column, you want to cover the hole in the center so it's not visible. To add the center brick, wait until you've put down the first 2 bricks in the final course. Then, lay the center brick and finish the rest of the course. If there are any joints you haven't smoothed out yet, wait until they harden to the point where they resist minimal pressure. Then, use your jointing tool to scrape off the excess mortar so they're flush with the bricks. Be careful you don't wait too long or the mortar could dry and you'll lose your chance to smooth out the joints. A capstone can be brick, concrete or stone, and it's put on top of a brick column to give it a nice, finished appearance. If you're interested in adding a capstone to your column, get one that's around 3 inches (7.6 cm) longer and wider than the column. Then, spread a layer of mortar on top of the column and center the capstone on top of it.  You can also make a brick capstone by using bricks that are larger than the ones you used in your column. Cut your bricks in half and lay them with their sides facing out for added strength and visual appeal.
Add a layer of mortar and wire mesh before the final course of bricks. Lay the final course of bricks, but add an extra brick in the center this time. Smooth out any remaining joints before the mortar dries. Top your brick column with a capstone if you want a polished finish.