After noting how easy it is to add a column with the SMILES representations of all molecules to your table in the DS Client, i was asked to demonstrate …
So here it goes:

1. starting from the Data Table of your molecules, add a new column to take up the SMILES: right-click on any of the column headers and select Add Attribute with the following parameters:
add to: Molecule
Name: {your choice}
Value: - leave empty -
Type: String

2. if at the left you don’t see the structures already, right-click on the index column and click Show Chemistry to display them.

3. go to Edit > Preferences… and verify that in Molecule Window the Ignore column titles option is checked.

4. click on the header of the Structure column to select it entirely and copy the contents to the clipboard (Ctrl-C or right-click > Copy).

5. select the header of the new column of step 1 and paste (Ctrl-V or right-click > Paste) the contents of the clipboard.

Done.

Note when using an older version of Discovery Studio, that the produced SMILES may have the wrong chirality; this known issue (DSC-27755) has been fixed in BIOVIA Discovery Studio 2018.