Hi Michal,

tricky point in your case is you cannot use 

dw_1.getItemString(row, 'symbol')

because 'X' is the *displayed value* instead of the *data value*.

So, you need to use the Evaluate + LookupDisplay functions. 
Put code below in the dataWindow rowfocuschanged event, so you trigger the filter only for the selected row:

datawindowChild ldwc
String displayedValue

dw_1.getChild('method', ldwc)
ldwc.setTransobject(sqlca)

displayedValue = dw_1.Describe("Evaluate('LookupDisplay(symbol)', " + String(currentrow) + ")")

ldwc.setFilter("symbol_column = '" + displayedValue + "'") 
ldwc.Filter()
ldwc.Retrieve()

Note that "symbol_column" is column in 1st DDDW where you have symbol's values.

In short, use GetChild() to get a reference to a DDDW, and use LookupDisplay() to capture displayed values instead of data values.

Best,

.m