An ellipse has two focal points (foci is the plural of focus) which are located on the major axis symmetrically around the center point. The Minor axis also passes through the center, at right angles to the major. I think you already have the semi-minor dimension as 0.378 so your problem is just to find the semi-major dimension.
Here is how I solved it. Draw an arbitrary ellipse centered on the origin. Place a point on the major axis above the center to represent one focus. Place another below the center. Constrain them to be symmetrical about the minor axis. Constrain the semi-minor axis to be 0.378. Constrain the distance from the top of the major axis to the upper focal point to be 0.307. For convenience I named this dimension 'a'.
Now we can solve for the position of the focal points using a property of ellipses that the sum of the distances from any point on the circumference to the two focal points is constant. We can solve this using simple trigonometry, or we can let Fusion solve it for us.
I created a dimension line from the upper focal point to the left end of the minor axis, and I made this a driven dimension. For convenience I named this 'b'. I created a dimension line between the two foci and defined it using the formula '2*(b-a)'. This is because the sum of the distances from the point on the circumference at the left end of the minor axis to both foci (a plus a) must the the same as the sum of the distances from the point at the top of the major axis to both foci (our unknown distance + b, plus b).
Adding another driven dimension to the sketch allows us the read off the semi-major axis as 0.386.
Now that I look at this I think there might be an easier way to solve it using the property that the distance from a focus to the point where the minor axis intersects the circumference is equal to the semi-major axis (both are 0.386 in this case). That probably allows for a solution using only constraints and no formulas.
I don't think there is enough information in your sketch to fully constrain the position of the ellipse with respect to the other features. Some dimensions appear to be missing.
