How to draw 45 degree Gann Line? thank you

You need to understand that there is no single "angle" that can be determined

in anisotropic charts, i.e. ones that X axis scale has different units than Y axis.

In price chart X axis scale is TIME where Y axis scale is PRICE (dollars).

There is no fixed mathematical relation between time and dollars, therefore there is no angle.

All charts use dynamic scale, and that means that relation between X and Y is dynamic

and arbitrary based on price movement, zoom factor, display area size, etc.

The concept of using fixed "angles" on the charts come from Gann.

Unfortunatelly all Gann theories involving angles are simply invalid because he "assumed" certain

relationship between TIME and PRICE say: one dollar equals one day.

He drawn his charts ON PAPER and ASSUMMED constant Y scale vs X.

Even such simple fact as inflation makes such constant relationship invalid.

Time vs price relationship is not fixed on computer where you can zoom in/out all the way all the time.

How would you define one day in EURUSD and how in say ES contract?

They would be totally different.