You can access a campaign's affidavits from the campaigns list options menu or from within the campaign page.
When you open the options menu it might take a few seconds for the View campaign affidavit menu item to be selectable; TAP checks to see if the campaign has delivered any impressions. If there are impressions to report, the menu item can be selected. If there is no delivery, the menu item remains greyed-out.
Alternatively, click Metrics in the TAP Applications menu to go to the Metrics interface in a new browser tab, then select TAP Explore > Affidavit > Affidavit Reports in the sidebar.
TAP Affidavits is described in the Triton Metrics User Guide.