How to use IN to compare a single value with a comma separated field in another column
There is a way to do this. However, I highly recommend that you reconsider using comma-separated values within a column. If you ABSOLUTELY must do it this way, you can use the LIKE operator with wildcards. This will enable you to search the attribute mask string for values. Expect terrible performance when looking up many values.

inner join AuditBase              t3
    on t2.ObjectTypeCode=t3.ObjectTypeCode
    and t3.AttributeMask LIKE '%' + convert(varchar,t1.ColumnNumber) + '%'
AuditBase)