Assuming that the document name remains the same after copying to the new library-
You can create a dynamic string variable to store the link like this: Document Title<a href="http://site/targetLibrary/currentItem[FileLeafRef]">Document Title</a>
.
currentItem[FileLeafRef] is the dynamic part of the string which you will need to get from the current item.
FileLeafRef is the internal name of field "Name" in the document lib.
You can then use this variable in your email body.