To help in/on these topics - offer help in/on these topics

Question

I wonder which preposition goes best with help in these phrases:

... people who ** could help **:

• in these topics
• on these topics

... people who ** could offer help**

• in these topics
• on these topics

I was typing a thank you comment in this post: Into and out of 'time out' for kids, but I felt I lost my bearings on which preposition to use; and when I quickly looked up on Google I didn't find immediate results. Google Ngram was not of much help.

I might get it right if I took a break and came back later but I thought I'd ask to test my guess and for future reference anyway- I guess phrases that pull up help/in/topic together sound familiar; and I'd venture a guess that the pattern offer help on these topics is the correct one.

Answer 1

Topics work with the preposition on. If X is part of topic Y, then X can be said to be "on" Y.

We are debating on this topic today.

Today's show is on construction materials.

Discussion is happening on WWII warfare tactics (topic = "WWII warfare tactics").