The task ID is randomly generated and therefore it will not be possible to procedurally generate a URL to email to approvers. Additionally, the table that stores the those IDs is request_backend which does not also store data about the transaction that is meaningful to humans. So, in order to query the DB to get the ID it will require knitting together data from several sources. Without querying other DB tables first it isn't possible to know which ID you want from request_backend.
CA Identity Portal Engineering has suggested opening this up as an enhancement request rather than pursuing the database query. However, your DBA may be able to make something that does what you're looking for.