This note was on Metalink, may help.
Creating DFF on the self service side can be quite complicated:
1- Navigate to the self service form you wish to add the DFF to
2- Click the About This Page link on the bottom left of the form.
If this link is not available, please set to yes the profile option FND: Diagnostics as stated in Note 275876.1 Oracle Application Framework Profile Options Release 11i
"Setting this to “Yes” causes a Diagnostics global button to render on every page. Select this button to view the log messages for the page. Enabling this profile also automatically renders the "About this page" link at the bottom of every OA Framework page."
3- Under the Page tab > Flexfield References section, a list of the flexfields which are supported by this page are listed. These are DFF for which you can Create an Item for. If a DFF you wish to add to the page is not in this list, then this page cannot have the DFF added to it without customising the code (which is not supported).
4- Under Page Definition, select the Expand All link. The View Object column lists all the possible values for the View Instance value. Depending on the DFF you are creating an item for, you are 'work out' the view that is most probable. That is, there is no direct way of finding which view is it out of the Views available under the View Object column.
5- Then create an item, via Personalize Page > Select Create Item at the appropiate level where you would like the DFF to be created. Ensure you enter in the values for:
Item Style: Flex
ID: <name of the new item>
Appl Short Name: (in HR for example it would be PER)
Name: (this is the name of the flexfield as it appeared under the About This Page Link, e.g.PER_ABSENCE_ATTENDANCES)
VIEW INSTANCE: this is the value you determined in step 4
You can then Use the Segment List to add each segment, use the wind pipe (|) to separate each segment.
Sahir