Generating a generic INSERT/UPDATE Trigger to conform data?
No, there is no generic, column-agnostic way to join the INSERTED pseudo-table to the base table. You will need to use a conventional inner join and reference the PK column (or columns if the key is composite) explicitly in the join predicate.

Therefore, if the PK column is not the same in each of the tables you are generating the triggers for, there is no way around querying metadata to find out the column name to use. You can do that using the SQL Standard-compliant (well, more or less) INFORMATION_SCHEMA views (example) or using the native SQL Server system catalogues (example).