Here are some resources that address the task and qualifications of elders, especially the qualification "able to teach" (1 Timothy 3:2; Titus 1:9).

David Mathis

Articles

• One Thing Sets Elders Apart http://www.desiringgod.org/articles/one-thing-sets-elders-apart
• Must Elders Be Skilled in Teaching? | Desiring God https://www.desiringgod.org/articles/must-elders-be-skilled-in-teaching
• Our God Is a Teacher at Heart | Desiring God https://www.desiringgod.org/articles/our-god-is-a-teacher-at-heart
• Pastors Teach : 9Marks https://www.9marks.org/article/pastors-teach/

Book

• https://www.desiringgod.org/books/workers-for-your-joy (pdf - https://www.desiringgod.org/books/workers-for-your-joy.pdf )

Jeremie Rinne

Article

• A Job Description for Lay Elders https://9marks.org/article/journaljob-description-lay-elders/

Book

• Church Elders https://www.9marks.org/books/church-elders/

Podcasts

• 9M Pastors' Talk: Episode 96: On Church Elders (with Jeramie Rinne) https://www.9marks.org/conversations/episode-96-on-church-elders-with-jeramie-rinne/
• Elders: Raising Them Up & Keeping Them Together with Jeramie Rinne and Eric Bancroft https://www.9marks.org/conversations/elders-raising-them-up-keeping-them-together-with-jeramie-rinne-and-eric-bancroft/

Other Articles

• Elders: Lead! https://www.9marks.org/article/elders-lead/
• What Does it Mean for an Elder to be "Able to Teach"? A Proposal http://www.nathanfinn.com/2012/06/27/what-does-it-mean-for-an-elder-to-be-able-to-teach-a-proposal/
• What “Able to Teach” Means and Doesn’t Mean https://www.9marks.org/article/what-able-to-teach-means-and-doesnt-mean/