Mechanism that checks the condition of value

How can I be able to create a script that always check’s the status of the NumberValue in example? Something like a loop?

You can use an event to do this. Additionally it is more efficient than a loop as events run only when the value is changed rather than every frame or second like in a loop. (This is polling which is considered bad)
Example code given:

local function printValue(value)
Workspace.NumberValue.Value = 20
--print 20 in Output

the global variable Workspace is deprecated, use workspace