How when using INDEX MATCH do I use OR when setting search array?

it would be very helpful if you could provide a sample workbook (no private info please).  If you can't attach/upload here then provide a public link to a cloud share solution like OneDrive or Google Drive.  A less but still helpful alternative is to provide pictures of the worksheets.

That said I think you are indicating that on the 'Data Sheet' you have task lines assigned to people based on initials in column J.  You want to do a lookup of that task based on those initials in column J but certain tasks you would like to have 2 or more people assigned to.

So i would like to note that you did tag with Office 365 so assuming you have the latest you have access to newer functions like XLOOKUP and FILTER.  So your above INDEX-MATCH could be done using XLOOKUP like:

=XLOOKUP("JB1",‘Data Sheet’!J:J,'Data Sheet’!B:B)

This assumed that the '2' at the end of the original formula was intended to return column 2.  Regardless, check into this function as I think you will find it very useful.

I also recommend checking out FILTER which for the above could be:

=FILTER(‘Data Sheet’!B:B, “JB1”=’Data Sheet’!J:J, "not found")

With FILTER you can easily return multiple rows and columns.  For example to return ALL of "JB" tasks it would be:

=FILTER(‘Data Sheet’!B:B, “JB”=LEFT(’Data Sheet’!J:J, 2) , "not found")

Now that doesn't solve your question about having multiple people but it can.  For example you can use XLOOKUP with wildcard characters:

=XLOOKUP("*JB1*",‘Data Sheet’!J:J,'Data Sheet’!B:B,"none found", 2)

then in column J you can enter "AB1, CD1, EF1, JB1, XY1" and it will find the JB1

similarly you can find every task assigned to "JB" using FILTER using something like:

=FILTER(‘Data Sheet’!B:B, ISNUMBER(SEARCH(“JB”,’Data Sheet’!J:J) ), "not found")

hope that helps.