The method most people use to select contacts for automatic journal activities, is to go to Tools, Options, Journal options and manually click each contact to include them in the automatic journal activities.
It’s clumsy and slow. The other method in that dialog is to use the space bar and down arrow – down arrow to move the cursor and the space bar to select it. It's just as clumsy.
A “Select all” option would be nice, but I don’t expect it will happen because most people don’t use the journal and of those who do, many don't want to journal every contact, only specific ones.
Fortunately, there is an easier way to select contacts for journaling. You can go to the Contacts folder and add the journal field to a table view – like phone list. Right click on the journal field and select group by this field. Drag items from the No and (none) groups to the Yes group. Or, with in-cell editing enabled, you can click in the journal field to enable it on specific contacts. (down arrow, space works here too)