You may have already learned that network addresses (routes) can be summarized. That is, many network addresses can be summarized (represented) by a single network address (i.e a route). A default route can be considered a summary route that contains all network addresses. Because routes can be summarized, routers may not have complete information about the entire internet, but they may have a route to a large summary network that contains the destination. That is, they know enough to forward the packet to another router that will have more information.
So if you send me data, your provider may not know where my IP address is located. But it may know that my IP is in the range of addresses that are located in the United States. So all your ISP needs to know is how to forward it to a router closer to the US. That router will have more information to get the packet closer to me. It in turn will forward to another router with more specific information, until the data gets to me.
The Tier 1 and Tier 2 providers that make up the backbone of the Internet have routers that carry routes to all the networks connected to the Internet (currently more than 500,000 routes). Your IP packet will eventually be forwarded to a router that does know to get to the destination network.
You seem to be confusing layer-2 and layer-3. Bridging is not routing. Bridging has nothing to do with layer-3 addresses, and routing removes the layer-2 addresses. Routers route packets, and bridges switch frames.
Routing happens at layer-3 with layer-3, e.g. IP, addresses. Routing routes layer-3 packets between networks.
Bridging happens with layer-2, e.g. MAC, addresses. Bridging delivers layer-2 frames directly from host-to-host on the same network.
If a packet is destined for a different network, the host will address the layer-3 packet to the destination host and the layer-2 frame used to encapsulate the layer-3 packet to the layer-2 address of its configured gateway (normally a router). A router will strip off the layer-2 frame, losing the layer-2 frame and addresses, inspect the destination layer-3 address on the packet, and forward the packet to the next interface, building a new frame for the next network.
Bridges that have all interfaces using the same layer-2 protocol, e.g. ethernet switches, are called transparent bridges, and they simply inspect the frame for the layer-2 address, switching it to an interface found in its MAC address table, or flooding it to all other interfaces if the destination MAC address is not in its MAC address table.
If a bridge connects two different layer-2 protocols, e.g. a WAP connecting ethernet and Wi-Fi, it must translate the frames between the different layer-2 protocols, and they are called translating bridges. They still use a MAC address table to determine the interface to which they will switch frames. Both ethernet and Wi-Fi use compatible 48-bit MAC addresses, so the addressing can remain the same, although the frames are different.
Bridging networks without NAT: how it's done?
NAT really has nothing to do with routing or bridging. NAT is simply translating either the source, destination, or both layer-3 addresses in layer-3 packets, which are never seen by a layer-2 bridge.
Remember, bridging is on the same network, routing is between networks, and NAT is translating addresses to other addresses.
You cannot use RFC 1918 (or some other) addresses on the public internet, e.g. to 8.8.8.8. Non-global addresses must be translated to public addresses before they are sent on the public Internet. Not all networks use private addressing, but any that do must use some form of NAT to translate private addresses to public addresses before sending packets to the public Internet.
Your WAP (access point) is simply a bridge, and the NAT happens somewhere else before the packets from your 192.168.0.0/24 network are sent to the public Internet.
Best Answer
The former. Different requests use different connections and bear no relation to each other, even if they're carrying completely identical data. There's no deduplication of application-layer data on any lower layer. This method is called unicast.
As @manish_ma has explained, multicast is a special distribution form to send the same server data to multiple clients. The difference is that it is not a request-response model but the transmission is initiated by the server (may be triggered by a client event). Clients can then subscribe to the multicast - and get a copy - or not.
However, multicast does not work on the open Internet, only in private networks. Sites like Youtube actually stream a separate flow to each client, even if many watch the same (live) video.