Here is the Doc from microsoft which gives your info about all the fields retrieved from crm.
I have used javascript and webapi to retrieve particualr Report.
Note: using webpi you can only retrieve report and it's definition and not Specific report data.
Link fir not retrieveing report data
var req = new XMLHttpRequest();
req.open("GET", Xrm.Page.context.getClientUrl() + "/api/data/v9.1/reports?$filter=name eq 'aktivit%C3%A4ten'", false);
req.setRequestHeader("OData-MaxVersion", "4.0");
req.setRequestHeader("OData-Version", "4.0");
req.setRequestHeader("Accept", "application/json");
req.setRequestHeader("Content-Type", "application/json; charset=utf-8");
req.setRequestHeader("Prefer", "odata.include-annotations=\"*\"");
req.onreadystatechange = function() {
if (this.readyState === 4) {
req.onreadystatechange = null;
if (this.status === 200) {
var results = JSON.parse(this.response);
for (var i = 0; i < results.value.length; i++) {
var reportid = results.value[i]["reportid"];
}
} else {
Xrm.Utility.alertDialog(this.statusText);
}
}
};
req.send();