<p>Cynthia Erivo already earned two best actress Oscar nominations for portraying Harriet Tubman and the green-skinned Elphaba in &#8220;Wicked&#8221; — not to mention her Tony-winning work in &#8220;The Color Purple&#8221; — but her latest film, &#8220;Prima Facie,&#8221; might be her most challenging</p>