Under deductions & credits, how would I record COBRA payment premiums?

COBRA is medical insurance obtained through your former employer's plan. they would be deductible as such on schedule A.

Consolidated Omnibus Budget Reconciliation Act

What deduction I can take for Cobra premiums when using Turbotax, 

Health care premiums that you pay, such as for COBRA insurance, are deductible as an itemized medical expense on Schedule A. 

However, if the total of your itemized expenses are not greater than the standard deduction for your filing status, there’s no tax benefit.  

Please see the TurboTax Help article Where do I enter my medical expenses? for guidance in entering your medical expenses.