See full tutorial on how to show a placeholder or a tooltip(shortdesc) in an ADF column filter header here : https://cedricleruth.com/how-to-show-a-tooltipshortdesc-or-watermarkplaceholder-in-an-adf-column-filter-header/

showAPlaceholderOrATooltipInAnAdfColumnFilterHeader.jsf.xml

<!-- Below an example table on with a column header filter customized to display a place holder and tooltip -->
<af:table value="#{bindings.YourVO.collectionModel}" var="row" rows="#{bindings.YourVO.rangeSize}"
	  fetchSize="#{bindings.YourVO.rangeSize}" filterModel="#{bindings.YourVOCriteriaQuery.queryDescriptor}"
	  queryListener="#{bindings.YourVOCriteriaQuery.processQuery}" varStatus="vs"
	  selectionListener="#{bindings.YourVO.collectionModel.makeCurrent}" rowSelection="single" id="T1" 
          styleClass="AFStretchWidth"
	  rowBandingInterval="0" columnBandingInterval="0">
  <af:column sortProperty="#{bindings.YourVO.hints.YourVoAttribute.name}" filterable="true" sortable="true" id="Tc1" 
             width="60">
    <!-- Add the following filter facet to modify the header column filter inputText component -->
    <f:facet name="filter">
      <af:inputText value="#{vs.filterCriteria.YourVoAttribute}" 
                    placeholder="YOUR PLACE HOLDER TEXT" shortDesc="YOUR SHORTDESC TEXT" id="id4">
      </af:inputText>
    </f:facet>
    <af:outputText value="#{row.YourVoAttribute}" id="ot1"/>
  </af:column>
</af:table>