<aura:iteration items="{!v.txList}" var="tl" indexVar="index">
<tr>
    <td>
        <div class="slds-truncate"  >{!tl.dateCreatedFormatted}</div>
    </td>
    <td>
        <aura:if isTrue="{!tl.status == 'Sent'}">
            <ui:outputCurrency aura:id="{!index}"  class = "red" value="{!tl.amount}" click = "{!c.handleRowClick}"/>
        </aura:if>
        <aura:if isTrue="{!tl.status == 'Received'}">
            <ui:outputCurrency aura:id="{!index}"  class = "green" value="{!tl.amount}" click = "{!c.handleRowClick}"/>
        </aura:if>

    </td>

    <td>
        <div class="slds-truncate" >{!tl.transactionId}</div>
    </td>
    <td>
        <div class="slds-truncate" >{!tl.status}</div>
    </td>

</tr>

handleRowClick: function(component, event, helper) {
    console.log("Row clicked");

},

<tr onclick="{!c.handleRowClick}">
  <!-- omitted for brevity -->
</tr>

<tr onclick="{!c.handleRowClick}" data-row-index="{!index}">
  <!-- omitted for brevity -->
</tr>

handleRowClick: function(component, event, handler) {
    var target = event.target;
    while(target && !target.dataset.rowIndex) {
        target = target.parentNode;
    }
    if(target) {
        console.log(target.dataset.rowIndex);
    }
}