I would like to know how to add a watchlist column which reports %b values for Bollinger bands set to  20 period Exponential and 2 standard. deviations.

Thanks.

In TC2000 version 7 (where you posted the question), you would create a Personal Criteria Formula for the Bollinger %b:

(C - AVGC20) / (4 * SQR(ABS(C ^ 2 + C1 ^ 2 + C2 ^ 2 + C3 ^ 2 + C4 ^ 2 + C5 ^ 2 + C6 ^ 2 + C7 ^ 2 + C8 ^ 2 + C9 ^ 2 + C10 ^ 2 + C11 ^ 2 + C12 ^ 2 + C13 ^ 2 + C14 ^ 2 + C15 ^ 2 + C16 ^ 2 + C17 ^ 2 + C18 ^ 2 + C19 ^ 2 - 20 * AVGC20 ^ 2) / 19)) + .5

Modelling Bollinger Bands (& Standard Deviation) in a TC PCF
How to create a Personal Criteria Forumula (PCF)
PCF Formula Descriptions
Handy PCF example formulas to help you learn the syntax of PCFs!

And then use it as a WatchList Column.

Customize the Information Displayed in the WatchList

In TC2000 version 12.2 (which you seem to use more than v7), you would add the Bollinger Bands %B indicator to the charts, adjust its settings as desired, then click on the Bollinger Bands %B indicator and select Show Values in WatchList.

Adding Indicators
Customizing Indicators
Setting Up WatchList Columns