You can not access data within blocks. For function blocks (FBs) you access the instance data block that is programmed in the block call. But as i mentioned, there are special access rules for safety related data. If i remember right, it is ok to read data blocks from the safety program but you have to keep in mind that the this program is executed asynchronous.
The addressing of flags is described in the manual M0.0 = MX0.0 (Area Flags=M, Data Type Bool = X, address 0.0).
Direct periphery access like PAW (periphery output) or PIW (peripherie input) is not supported by Ignition. Apart from that, direct access to periphery addresses from a HMI is almost always a bad idea. Periphery access means that the processor stops what is is doing and tries to read the current state of the I/O module regardless of the program cycle.
You may check if PQW300 is in the processors output image. If this is the case, you can use QW300 (or QI300) instead. Of course this only works if PQW300 is a non-safe output.
There is no support for symbol import to Ignition. A few possibilities have been discussed in this thread. But: you don't want to import all data blocks to Ignition's OPC-UA server. The server will start to poll all imported tags, and polling all data blocks will probably overload your processor's communication ressources.
If this is the only Siemens processor, you may use the processor integrated OPC-UA server that is offered by Siemens. There are also 3rd party servers with full support for browsing, symbolic addressing and the new security mechanisms. The Ignition driver uses the backward compatible S7-300 mode of modern processors.