I'm not fluent by any means, so if any native speaker wants to correct me, please do! I would also like to learn. But anyways, the way I would say this is... 고구마에 대해서 말하고 있었어. Here, the grammatical form that means "about" is "~에 대해(서)", which you attach to nouns. The "~고 있다" form, in case you do not know about it, is simply the progressive from (I am doING, I am eatING, etc.), conjugated into the past tense. I hope I was of help! ^-^

I don't fully understand the question, but I will try answer :) Was talking, suggest past-tense So you could use an example such as: I was discussing (topic) with my friend (name) e.g. "I was discussing sweet potatoes with my friend John" or informally "I was chatting to my friend John about sweet potatoes" If present tense, change ""I was" to "I am" or "I'm" If future tense, change ""I was" to "I will be" Hope this helps, If you wish to re-phrase the question I can try help more. M

I agree with Won. There are grammar points specifically for "about", but here it would feel a bit strange to use them. I agree that creating a little adjective phrase sounds better (고구마 먹는 이야기). While I might not have come up with that on my own if I had tried, I did think that using 에 대한 would sound unnatural. So 0.5pts for me :) Lol 열심히 공부하세요~

It's fine! Thank you Won~^^

Hello, Although it's said that "about" means ~에 대해서 or 관해서 in Korean, which is right in most sentences, but I don't feel 고구마 먹는 것에 대해서 말하고 있었어 sound native or natural to me. It does depends on the situation but I would say 고구마 먹는 이야기 하고 있었어. I'm sorry I can't completly expain it.