You must has installed a tweak or theme that removes the clock (there are many, many tweaks and themes that do this. Many.).
By any chance, do you have Springtomize 2 installed? There is an option in its settings (in the Settings app) that allows you to stop the clock from showing (it's under the Lockscreen tab in Springtomize's settings). Check to make sure you haven't accidentally turned ON the "Hide Top Bar" function - because turning that on, while it does indeed hide the top black bar, also hides the clock. If that's the case, turn that setting OFF and then re-spring. Your clock should come back.
If that's not it - could you list the tweaks you have installed? Maybe we'll be able to recognize one that is hiding your clock. Again, there are so many ways to hide the clock; we'll need a bit more info on what you have installed.
Marilyn