?SYS(14, nIndexNumber [, nWorkArea | cTableAlias])
or
? KEY(nIndexNumber)

The filtered index expression:
?SYS(2021, nIndexNumber [, nWorkArea | cTableAlias])

Also ataginfo() for VFP7 and above.

>I can get all of the tag names for a specific table using the tag() function. What I want to do it find out the actual index for that tag. Example: If tag(1) = "MYORDER" I want to find out which field(s) the tag MYORDER is indexing. How can I do this programmatically?