can we also add a note to the card as to why blocked?

[Satyajit Baral]

when moving cards into the Blocked column/ existing column, can we also add a note to the card as to why it is now blocked?

I have already a column as blocked. I used a feature in Rally where I was able to add notes with a red tag 🏷 stating a reason! 

[KAGITHALA BABU ANVESH]

I Agree with @Jack Brickey ,

Place a Transition screen with Multiline "Comment" or "Note"  field on which transition is incoming to "BLOCKED" Status.

When card moving to Blocked, The transition screen will be populated and you can enter the required in formation.

Thanks,

Anvesh

[Satyajit Baral]

Thank you! I am not sure how to add transition layer as I think it might impact other boards. As the same workflow of copied across different development teams. I am only trying to implement for one board. 
alos I did not find any you tube video or a good link which guides step by step to create a Transition.

so, as a short term fix I have added a blocked swimlabe, added a label then set a query to short the cards. 

[KAGITHALA BABU ANVESH]

Board Swimlanes are configured by using workflow status.

you only able to create a "Transition scree" in workflows only , not in boards

[Satyajit Baral]

Got it, thank you. Then it would not suffice my need. As only one development  team has requested this feature so it cannot be done. 

[Daniel Ebers]

You are right when you say that it would affect other projects (and implicit that means: other boards, too) when you would adjust their workflow.

But you can copy their workflow and workflow scheme and then assign it to *just* the project that wants to use the transition screen exclusively.

That means: the requirement is met but other projects are left untouched.

This part of documentation should help to get some idea:
Manage Issue Workflows:
https://support.atlassian.com/jira-cloud-administration/docs/manage-issue-workflows/

Manage Issue Screens:
https://support.atlassian.com/jira-cloud-administration/docs/manage-issue-screens/

[Jack Brickey]

You could add a screen to the transition that would allow the user to add a comment.