Once you have set up a dialogue topic in the TESCS, you may find that you still can’t talk about it with the NPC you have given the dialogue to, because for the game you don't know that particular topic yet. There are two ways to change that condition: either you introduce the topic in another conversation topic (e.g. a custom greeting) or you give it to the player via script, which makes sense when it’s an obvious topic the player would ask about without being brought to it by conversation (e.g. if you see and NPC standing under a waterfall, you might want to ask him about "aren't you getting wet?" even if the NPC doesn’t bring up the topic.
To do that, just attach a small script to the NPC:
Begin AddSpecialDialogue
;add possibility to ask about travel
AddTopic, "aren't you getting wet?"
End AddSpecialDialogue
Note: You must already have the topic with this topic ID set up before you make this script, otherwise the script compiler will complain.
Even if a topic is introduced through dialogue, it may also be useful to use AddTopic in the resultbox of the line that introduces the topic. If another mod adds a topic with the same ID or an ID of which your topic's ID is a subset, your topic may not be hyperlinked, but AddTopic will ensure that it appears in the speaker's topics list anyway.
AddTopic adds the topic to the player's "known topics" list. So using
"Actor_ID"->AddTopic "blabla" is wrong: an NPC's known topics are entirely predefined by speaker conditions.
You can not remove a topic via script; you can however set a speaker condition in the Dialogue editor which can be set from script (e.g. a variable or journal entry), which can be used to achieve the same effect.
