I am not sure if you are referring to Linking tickets by the jira definition, or if you just want to see them in the backlog..
If you mean Link tickets in the Jira way you enter the link dialog and choose the link type, and then the tickets will be linked to each other.
Otherwise, you would edit the Scrum/Kanban board to include both the existing project and the new project in the general setting for the board. Board Settings -> General -> Edit Filter Query.
Hello @Gaurav Joshi
Your description is ambiguous.
Because as per Jira terms, you can link issues(tickets) across projects if you have "Link isssue" permission in respective project.
Thus, it will be great if you elaborate more on what you need, may be with a screenshot.
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