I studied the same question and found this almost 2 year old thread. I will leave my results here for those who are looking for answers:
There is no convenient way to manually enter the coordinates of a control point, but there are 2 alternatives:
easy:
When dragging around a control point, you can see that the control point is displayed in the status bar below:

If you zoom in enough, you can place it with fairly high accuracy.
difficult:
- Open the appropriate path in the XML editor:

- Select attribute
d . This attribute describes a path using nodes and control points in a single line of numbers. - First, the coordinates of the nodes (X / Y) are indicated. After that you will find the letter
C indicating the origin of the control point (X / Y). - Edit the points manually and click the "Install" button as soon as you are done. Note. The units used here may differ from the units used to display your page. In this case, you will have to calculate the additional offset.
pixelperfect
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