Find specific attached disk, not volume, by Applescript
I'm not that great in writing Apple scripts but here is an idea how to solve your problem.

In the first method outlined below I search the device tree of system_profiler to get the DiskIdentifier of a disk device attached to the USB3 card reader built into your Dell monitor. In the second method I use ioreg.

system_profiler:

To get the DiskIdentifier of a SD-card attached to the external SD-Reader use something like:

system_profiler -detailLevel mini | grep -A 30 0x0307 | awk '/disk/ {gsub("BSD Name:", ""); print $NF}'


with grep -A 30 0x0307: output the next 30 lines after finding the string 0x0307
and awk '/disk/ {gsub("BSD Name:", ""); print $NF}' to get the disk number but remove BSD Name: from the output.

The command takes about 10 seconds on my system.

You may have to adjust the value of -A and the characteristic string (in the example above I used your USB3.0 Card Reader Product ID: 0x0307). Check the device tree with the app System Information and search for an appropriate string.

Wrap all that in a variable like $SDDiskToErase and hand it over to your diskutil eraseDisk command.

Using the above slightly modified line I got the diskIdentifier (disk2) of an external USB disk directly attached to my Mac:

system_profiler -detailLevel mini | grep -A 30 0x1c26 | awk '/disk/ {gsub("BSD Name:", ""); print $NF}'
disk2


ioreg:

Another initial command is ioreg -l | grep … (… is similar to the above) which is much faster (less than a second).

Attach an SD-card and get its DiskIdentifier with diskutil list. Then make a dump of ioreg with ioreg -l &gt; ~/Desktop/ioreg-dump.txt.

Search in ioreg-dump.txt for the diskIdentifier found above. The disk is connected to a superior controller (the one in your monitor) visualized by the long vertical and short horizontal "lines" on the left in the dumb file. Use a characteristic and unique string of the controller like a serial number, IOName, deviceID etc. Then choose a number of subsequent lines for -A big enough to contain the diskIdentifier (e.g. disk6) but small enough not to contain the volume identifiers (e.g. disk6s1).

Example:

ioreg -l | grep -A 350 0x100000214 | awk '/disk/ {gsub("\"",""); print $NF}'
disk2


To use the command in Apple Script you have to escape all inner " and \:

"ioreg -l | grep -A 10 SD/MMC/MS/MSPRO | awk '/disk/ {gsub("\"",""); print $NF}'"


becomes:

do shell script "ioreg -l | grep -A 10 SD/MMC/MS/MSPRO | awk '/disk/ {gsub(\"\\\"\",\"\"); print $NF}'"