I always hear people talkings about compounding interest in videos. Is investing in robo-advisors counted as compounding? doing Dollar cost averaging is not compounding?

Compound interest refers to getting interest on the interest from your intial investment.

Dollar cost averaging is simply the method of investment as compared to lump sum (one-shot) and does not affect whether your returns are compounded.

In the case of robos, if returns, in the form of dividends, are re-invested then there will be compound returns. ​​​