How can I tell where is the guiding sensor with respect to the image I see on the computer screen ?In other words if I am looking at my image on CCDOps on my computer and I want to place a star on the internal guiding sensor, how can I tell the location of the internal sensor ?
This depends on the orientation of the star field relative to the position of the camera on the scope, and the optical configuration of the telescope. The TC-237 guide sensor will be above or below the rectangular long axis of the KAI-2001C sensor. There is a small mirror there to send the starlight from the guide star to the guide sensor, so there is an additional reflection. You'll have to work this out for your particular setup. If you are using MaxIm DL instead of CCDOps, you could plate-solve both images to get their precise location and orientation. Then you could work out the field-of-view and orientation.
The sensor is above your main image. Where it is on the sky depends on the orientation of your camera to your optical system. On my two Newtonian scopes with the ST-2000, with the scope pointing straight up and the focuser is on the west side and the camera mounted to the focuser with the connector end in the 3:00 position, the image is "north up." Other optical trains will be different. Planetarium programs such as the SkyX pro, has FOVIs or Field Of View Indicators for the ST-2000 as well as the eyepieces for your optical system. You can rotate the FOVI as well as the sky chart. You can even do mosaics with that for larger objects.
Tip: The quick way to find the orientation of your guide sensor is to target the moon. It's large enough to see in both chips at the same time. You can find the limb of the moon and then the orientation becomes much more obvious.
