Unfortunately other that AstuteGraphics or Esko, there is no such tool. There are two ways you can check, but I know they are not what you want. You can normally Open an Ai file in AcrobatPro and use the Output Preview from there, where you have all Separations and Total Ink Coverage, but it is not live while editing. The other option is to have an InDesign file open with the Illustrator image placed, and use the InDesign panel… when you make a change you can save the file… switch to InDesign and measure (Note this also is dependent on Colour management settings in InDesign) I think this is a long standing feature request, but illustrator is used for so much more than print and has not received that yet. Please verbalise your need and why it is important to you in Adobe Illustrator Feedback
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