The Web2Bookmarks portlet stores the bookmarks in the portlet preferences. These portlet preferences should be stored in the customization domain. You can also see the Web2Bookmarks preferences using XMLAccess. If you export out a page with a portlet instance, you should see the bookmark data there:

 <portletinstance action="update" domain="cust" objectid="Z5_189IG182K8ICD0AEVJO49V00O4" owner="uid=userone,o=defaultWIMFileBasedRealm" parentref="Z5_189IG182K8ICD0AEVJO49V0087" portletref="Z3_CGAH47L00OJ790IAH1AFAN10M7">
                             <preferences name="bookmarks" update="set">
                                 <value><![CDATA[{length:1,items:[undefined,{name:'IBM',url:'http://www.ibm.com/us-en/',parent_id:'-',external_Or_internal:'E',creation_date:1448300394841,last_modified_date:'',pageName:'',isFolderOrLink:function (){          return "link";       },setName:function (aname){           this.name=aname;           return true;       },getName:function (){           return this.name;       },setUrl:function (aurl){           this.url=aurl;           return true;       },getUrl:function (){           return this.url;       },setParent_id:function (parentname){            this.parent_id=parentname;            return true;       },getParent_id:function (){            return this.parent_id;       },setExternal_Or_internal:function (flag){            this.external_Or_internal=flag;            return true;       },getExternal_Or_internal:function (){            return this.external_Or_internal;       },setCreation_date:function (date){           this.creation_date=date;           return true;       },getCreation_date:function (){           return this.creation_date;       },setLast_modified_date:function (date){           this.last_modified_date=date;           return true;       },getLast_modified_date:function (){           return this.last_modified_date;       },setPageName:function (page){            this.pageName=page;            return true;       },getPageName:function (){            return this.pageName;       }}],fllength:2,removeItem:function (key)  {   if (typeof(this.items[key]) != 'undefined') {    this.length--;    delete this.items[key];   }        return true;  },getItem:function (key) {   return this.items[key];  },setItem:function (key, value)  {   if (typeof(value) != 'undefined') {    if (typeof(this.items[key]) == 'undefined') {     this.length++;    }     this.items[key] = value;   }        return true;  }}]]></value>
                             </preferences>