Question

If any documents stuck in Verification queue, Is there any option to send an alert via email stating the document stays in queue long time.

Answer

The workflow schema has SLA settings for processing inside FlexiCapture project:
Project Setup Station > Project > Properties
 

Although the SLA settings don't have an inbox possibility to send e-mail notifications, so its functionality can also be implemented via script: 

Where you may use .NET references for work with e-mail:
 
Please note that the interface IBatch (which is main during SLA script development) has the property StageInfo which points to the batch's current processing stage: