Before saving, you should click the crop tool, Select "Fixed Aspect Ratio" in the drop down, and then select "8x10 (Landscape or portrait as needed) from the other drop down, or if not available enter "8x10" in the custom size inputs. Now draw a crop rectangle around the crop you want and then double click inside the cropped area to "fix" the crop.
1. With the image open in CNX2, from the top menu click Edit|Size/Resolution
2. Click the "Resample image" radio button
3. Enter '10' in the width and select "inches" if not the default
4. Enter '300' in "resolution" and select "DPI" if not the default
5. Click "Apply" in the Size/Res edit step
Your image size should now be 3000 x 2400, which is 8x10 at 300dpi
6. You should now add a USM sharpening step, with a modest amount of sharpening, something like 15/5/0 or thereabouts will probably be about right but this is certainly subject to taste. Click Adjust|Focus|Unsharp Mask... to initiate this step. This MUST be done AFTER the re-size step.
7. Click File|Save As... from the menu.
8. Give it a name and select folder. File Type = "Jpg" from the drop down
9. On the pop up screen, slide the quality slider to 100%. This would be equivalent to a highest quality JPG. I forget the max value of Photoshop, which I think you are referring to as "quality 10". If some other number, and you do not want the highest quality, fudge it .
If you are trying to save an image in some equivalent to Photshops's quality scale, other than highest quality, or some other editor, the easiest way is probably to save in both editors, using different CNX2 quality settings, until the file sizes are roughly similar. Higher quality is always a larger file so they are roughly proportionate. They are doing the same thing, just using different scales.