First go to your comments page, then click the comment you want the url of an then copy the URL that's in the search box. It should be something like https://steemit.com/bitconnect/@miguelportela/bitconnect-token-is-crashing-is-this-the-beginning-of-the-end-for-their-hard-to-sustain-model#@bloodypizza/re-miguelportela-re-bloodypizza-re-miguelportela-bitconnect-token-is-crashing-is-this-the-beginning-of-the-end-for-their-hard-to-sustain-model-20170825t095222793z . See? Then you just copy that into the memo instead of a regular post URL.