I need Exactly Unicode equivalent as U00AE.

That doesn't make any sense. Please speak in terms of HTML entities, Unicode characters, U+xxxx notation and perhaps UTF-8 encoding.

• Are you asking how to get character U+00AE from "®"?

  decode_entities will get the character from ®.

• Are you asking how to get the string "U+00AE" from character U+00AE?

  ord will get 0xAE from the character.

  sprintf can be used to format 0xAE as hex.

For example,

>perl -MHTML::Entities=decode_entities -e"printf qq{U+%04X\n}, ord(dec
+ode_entities('®'))"
U+00AE
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But then again, you also mentioned JSON. Whatever JSON module will handle serializing the character as "\u00AE" or similar from from the character U+00AE, so all you only need is decode_entities.