Datasheet Notation for Filter Parameters
If you look at the equations right below the schematic you will see that all of the terms are defined:
fi = fCLK/20 where fCLK is the input clock frequency.
f0 = center frequency of the filter (fo is defined earlier in the data sheet as being the center frequency of the filter).
fn = fo.
That is enough information to be able to compute all of the required values. It is true that they don't explicitly define the meanings of fi and fn but their values are easily computed from the given equations.