First of all what is the use case for wanting to post that to a DataTable?
As Polina pointed out, you have full access to the logs through associated services.
If you want to log to a DataTable, you can just do it through a Service directly.
If you have trouble with creating services or adding services to mashups, I recommend you attend a Thingworx Fundamentals training or go through the eLearning.
I gone through the tutorials and analyzed that those are ThingWorx logs But we are looking for below scenario.
Want to send our own system generated events/logs to the ThingWorx server and want to display those in the appropriate Mashup. Here events are basically my system logs and want to send those logs to ThingWorx server using ThingWorx REST API.
In order to do this, you'll need to create a DataTable or a Stream in ThingWorx, with an associated DataShape that probably will consist of only 1 Field, the MessageLogText.
Then you'll create a service that'll take 2 parameters, Timestamp and MessageLogText, and using these two, will make inserts in the ThingWorx DataTable or Stream.
Key here is that this service you'll create will be automatically REST-ified, so you can call it from your DB.
That's one way of doing it, but take care that if the TW server will be offline then the REST calls to it will obviously fail.
Another method would be to store the messages in some DB, and then use some very simple SQL services only in order to display the data in your mashup, not necessarily storing it.
A Mesage Queue broker is also another alternative, so as soon as you insert a message, you can trigger an Insert into your TW storage with your message content. In order to do this you would need to develop an simple extension that will act as a Listener for the queue.
Hope it helps,