On 4.2, it's called a "widget" and (if you have the bottom bar showing at all) there should be a "bean" at the far right-hand side that you can click. Left-click that, select "Add widgets,' and add the "task manager" widget back into the panel. Note that, if you select the "Panel settings" menu item, you can move the location of the taskbar (after you add it) to be wherever you want it to be.
Oh, if you somehow removed the whole panel, right-click on the screen and select the "add panel" item. That will create a new panel for you (at the top of the screen, but you can move it to wherever to wan it located.) Then you'll need to add any widgets you want (task manager, application launcher, etc.) to the panel.