Where to find out rental loss amount for the prior year ? On prior year Sch E or on form 8582?

Your total loss is on Line 21 but that's not necessarily your deductible loss.

On Sch E

Line 21, 6198 loss

line 22, 8582 loss 

Line 21 and line 22 can be different if taxpayer AGI is less than 150K

line 26, total income or loss, if no other passive income to offset passive loss, this line would be entered"0"

On 8582 form,  page 1, part IV line (e) is the data that needs to be carried over to the next year. 

Please let me know if I am wrong.