You can do it either by using linked Rich Text Content Controls or by bookmarking the first instance and then using a Cross-Reference field to that bookmark for the second instance.

In my opinion, the Rich Text CCs is a superior method for two reasons:
1. Either instance can be edited to change the other
2. The changes are reflected in the other instance as soon as your cursor leaves the CC.

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Andrew Lockton
Chrysalis Design, Melbourne Australia