Where to waterproof?

Sounds like an older dwelling with concrete over brick under shower with a timber floor outside the shower.

Waterproofing should be:

For shower with hob, you need to waterproof the whole base and run the membrane down into a puddle flange in shower waste. The wall to floor interface should be waterproofed to a hight above the hob, say 50 mm above. The hob must be fully sealed, inside outside and on top with an overlap onto the floor outside. The internal corners must be sealed to 1.8 m from the shower wall to floor interface. Ant joins in the wall sheets must also be sealed as should all wall sheet fixings.

The wall should be sheeted with a water resistant sheet like Villaboard.

Timber floors must be sheeted with tile underlay sheeting and fully waterproofed right down into a puddle flange as the waste outlet.

Hope this helps.

Good luck.