You can't find it in the .acsm. The .acsm is downloaded before the book is associated with an AdobeID;
its association with the ID is created when the excrypted .epub file is created/downloaded, and held at the server end.
However, you can find the AdobeID (at least in internal form) from the .epub file.
To see the AdobeID from an encrypted .epub file:
- Open the file as a zip archive.
If you have a good zip archive manager like 7zip you can do this directly.
Otherwise, you must rename the .epub file to a .zip file to open it. - Find the file rights.xml inside the zip; probably META-INF\rights.xml
- Inside that file, you will find a section that looks something like <user>urn:uuid:ff2ddc22-eca0-46c6-a84d-xxxxxxxxxxxx</user>
- That is the AdobeID.
The ID was stored only in its internal form, and not by the username that belongs to the ID.
However, if you are on ADE2.0 you can use Help/Authorization Information (ctrl-shift-I, cmd-shift-I on Mac) which will show you both the external username and the internal ID.
At least you can check that way if ADE thinks you have the correct AdobeID for the book; but if you haven't it won't remind you of the username you used.
I don't know if Adobe service are able to find the userid if you can give them that internal ID.