CAN I CHARGE MY POWER BANK USING THE MOBILE CHARGER?

It entirely depends on what your charger and powerbank are rated at, but: as a rule of thumb, if it uses USB, then the answer is very likely a yes.
Keep in mind that, depending on the powerbank’s capacity and the phone charger’s rated output. The powerbank may place a load on the charger which the latter will not be able to fully satisfy safely:

the powerbank may not charge fully,
the charger may become hot, or shut itself down due to overcurrent, and
the charging process may take a very long time to complete (assuming it ever does).
Cheap knock-off chargers that are known to catch fire may catch fire during this process. But the probability is generally low. 😉
Additional note: be aware that some very old chargers designed to work with Nokia feature-phones (the ones with physical keyboards) may use a micro-USB port. But actually deliver ~3.8V (which is not only incredibly insufficient, but also wildly outside of USB specification). This is due to the fact that Nokia has historically been caught using the micro-USB port as a feature port combo (back in the days when they still used 3.8V to charge their batteries). Notably, all of such chargers I’ve seen have the cable moulded into the charger.