Hi Guys i got solution
here it is,
<t:dataTable id="insertTaskDataTable" border="1"
value="#{insertTask.taskList}" var="taskInfo" rowIndexVar="row"
iterationStatusVar="it" rendered="#{insertTask.taskList[0] != null}" >
<t:column>
<f:facet name="header">#{bundle['GROUP_HEADER']}</f:facet>
<h:selectOneMenu id="taskGroup" value="#{taskInfo.groupList.comboValue}" onchange="document.getElementById('addTask:insertTaskDataTable:#{row}:groupButton').click();">
<f:selectItems value="#{taskInfo.groupList.comboValues}" />
</h:selectOneMenu>
</t:column>
<t:column>
<f:facet name="header">#{bundle['CATEGORY_HEADER']}</f:facet>
<h:selectOneMenu id="taskCategory" value="#{taskInfo.categoryList.comboValue}" onchange="document.getElementById('addTask:insertTaskDataTable:#{row}:categoryButton').click();">
<f:selectItems value="#{taskInfo.categoryList.comboValues}" />
</h:selectOneMenu>
</t:column>
<t:column>
<f:facet name="header">#{bundle['ACTIVITY_HEADER']}</f:facet>
<h:selectOneMenu id="taskActivity" value="#{taskInfo.activityList.comboValue}" onchange="document.getElementById('addTask:insertTaskDataTable:#{row}:activityButton').click();">
<f:selectItems value="#{taskInfo.activityList.comboValues}" />
</h:selectOneMenu>
</t:column>
<t:column>
<f:facet name="header">#{bundle['SUBACTIVITY_HEADER']}</f:facet>
<h:selectOneMenu id="taskSubActivity" value="#{taskInfo.subActivityList.comboValue}" onchange="document.getElementById('addTask:insertTaskDataTable:#{row}:subActivityButton').click();">
<f:selectItems value="#{taskInfo.subActivityList.comboValues}" />
</h:selectOneMenu>
</t:column>
<t:column>
<f:facet name="header">#{bundle['COMPLEXTIY_HEADER']}</f:facet>
<h:selectOneMenu id="taskComplexity" value="#{taskInfo.complexityList.comboValue}">
<f:selectItems value="#{taskInfo.complexityList.comboValues}" />
</h:selectOneMenu>
</t:column>
<t:column>
<f:facet name="header">#{bundle['BENCHMARK_EFFORT_HEADER']}</f:facet>
<t:outputText value="#{taskInfo.benchMarkHrs}" style="height: 10px; width: 50px;" />
<t:outputLabel value=" hrs"/>
<t:outputText value="#{taskInfo.benchMarkMin}" style="height: 10px; width: 50px;" />
<t:outputLabel value="min"/>
</t:column>
<t:column>
<f:facet name="header">#{bundle['DESCRIPTION_HEADER']}</f:facet>
<t:inputText value="#{taskInfo.taskdescription}" />
<h:commandButton id="groupButton" style="visibility:hidden;display:none" actionListener="#{insertTask.handleGroupChange}">
<f:attribute name="groupid" value="#{row}" />
</h:commandButton>
<h:commandButton id="categoryButton" style="visibility:hidden;display:none" actionListener="#{insertTask.handleCategoryChange}">
<f:attribute name="categoryid" value="#{row}" />
</h:commandButton>
<h:commandButton id="activityButton" style="visibility:hidden;display:none" actionListener="#{insertTask.handleActivityChange}">
<f:attribute name="activityid" value="#{row}" />
</h:commandButton>
<h:commandButton id="subActivityButton" style="visibility:hidden;display:none" actionListener="#{insertTask.handleSubActivityChange}">
<f:attribute name="subactivityid" value="#{row}" />
</h:commandButton>
</t:column>
</t:dataTable>