Trigger creation for Sybase SQLAnywhere 16
I think the problem you are running into is caused by getting a mixture of T-SQL (ASE) syntax and SQLA (Watcom) syntax. You can use T-SQL triggers in SQLA - but with quite a lot of limitations. It better to do a re-write if you can.
This complies, whether it works, I have no idea! (The changes are all in the DECLARE statements. One per variable, double quotes removed from the timestamp datatype (as per markp-fuso's comment). If you really need local variables further down the code, you have to declare them at the beginning of a new BEGIN / END block)
create trigger DBA.WKM_autoFillCL143 after insert order 2 on DBA.Case_Checklist
  when ((select top 1 inserted.code from inserted) in( '143' ) )
  begin
    declare @parentRef integer; 
    declare @desc varchar(255); 
    declare @desc1 varchar(255); 
    declare @checkID integer;
    declare @tabid integer;
    declare @recProvider varchar(255);
    declare @recsRequested varchar(255);
    declare @dateFrom datetime;
    declare @dateTo datetime;
    set @parentRef = (select top 1 parent_ref from inserted);
    if (@parentRef &lt;&gt; '0')
      then
        set @desc = (select description from case_checklist where checklist_id = @parentRef);
        if (@desc is not null)
          then
            set @checkID = (select top 1 checklist_id from inserted);
            update WKM_RecordChecklistMapping set c143 = @checkID where c142 = @parentRef;
            set @tabid = (select top 1 tab_id from WKM_recordChecklistMapping where c142 = @parentRef);
            set @tabid = (select top 1 tab_id from user_tab2_data where tab_id = @tabid);
            if (@tabid is not null)
              then
                set @recProvider = (select top 1 Provider_Name from user_tab2_data where tab_id = @tabid);
                set @recsRequested = (select top 1 Records_Requested from user_tab2_data where tab_id = @tabid);
                set @dateFrom = (select top 1 For_Dates_From from user_tab2_data where tab_id = @tabid);
                set @dateTo = (select top 1 Through from user_tab2_data where tab_id = @tabid);
                set @desc1 = 'Receipt '+@recProvider+' Records? '+@recsRequested+', dates '+coalesce(convert(varchar(255),@dateFrom,1),'00/00/00')+' to '+coalesce(convert(varchar(255),@dateTo,1),'00/00/00');
                set @checkID = (select top 1 checklist_id from inserted);
                update case_checklist set description = @desc1,staff_assigned = 'ZKS',due_date = (today()+7) where checklist_id = @checkID
              end if;
          end if;
      end if;
  end;