<aura:component controller="mevLCaseComment" implements="flexipage:availableForRecordHome,force:hasRecordId" access="global" >
    <aura:attribute name="commentList" type="casecomment[]" />
    <aura:handler name="init" value="{!this}" action="{!c.doInit}" />
    <aura:iteration items="{!v.commentList}" var="cc" >
        {!cc.Id} - {!cc.commentbody} <br/>
    </aura:iteration>
</aura:component>

({
   doInit : function(component, event, helper) {
     var action = component.get("c.getCaseComments");
     var rcid = component.get("v.recordId");
     action.setParams({ "ccid" : rcid });
     action.setCallback(this, function(data){
       component.set("v.commentList",data.getReturnValue());
     });
     $A.enqueueAction(action);
   }
})

public class mevLCaseComment {
    @AuraEnabled
    public static list<casecomment> getCaseComments(id ccid) {
        system.debug(logginglevel.info, 'MEVION DEBUG: case id ' + ccid);
        return [Select Id, commentbody From casecomment Where parentid = :ccid];
    }
}