How do I open this door without the key? The toilet got locked from the outside and I don't have it's key.Any answers?

Anything that fits in that slot to turn it should open the lock. If that doesn't work, smashing the knob should get you in. That type of privacy lock sells nearly everywhere for about $10.00 and you can install it in a few minutes with a screwdriver.

It's illegal to have any bathroom doors that "lock from the outside" in most building codes (to prevent anyone from becoming trapped inside). Are you sure it wasn't actually "locked from the inside"? Anyway, turn the slotted latch in the center of the knob and it will lock from that side.

with a large3 flat screw driver and turning the centre part

Center of nob has a slot, use either flat head screw driver or coin to turn it to unlock .

First try turning the slot. If that don't turn. A hacksaw blade. Cut around the metal in front of the door flange. Twist off handle. Remove flat rod. Take screwdriver and move lock inside to open. Remove lock. 2 screws & replace with a better lock.

that would depend on the lock. Some inside doors, like bedroom and bathroom doors have a small hole in the door knob. All you need is a thin long nail or some other thin long item and you push that gently into the door knob and when you feel resistance, push a little harder and it will unlock the door.

looks like a standard straight blade screwdriver, large size, will do the job. If not, you'll likely have a choice of what to break -- the doorknob [by drilling out the lock mechanism] or the door frame or door [by whacking the door just above the knob with a sledge hammer or similar [a piece of wood between the hammer and the door might save the door and allow you to transmit the force tot he door frame].

Another idea would be to spread the door frame wider using a truck jack and block until the door pops open. If you're lucky, the frame wasn't shimmed out directly behind the latch area and this will let the latch pop open.

PS: replace the door knob after this -- you've had your lesson. After I had this lesson with my youngest grand, I swapped the knob with one from the pantry, carefully putting the locking mechanism inside the pantry [where no child can fit while closing the door] and leaving the bedroom [in this case] door unable to lock at all

Yes, get a locksmith.

Use a butter knife or a screwdriver in the slot to turn it. Door is unlocked.