To answer your question, I guess anything that applies to a market where there is a big rise of newcomers. Like new programmers and coding bootcamps.

If I only knew, I wouldn't tell you. I think what makes sense is to check out what thing was already growing in 2018 and will still be growing in 2019, but entry is relatively easy. Also if there is a possibility that this thing is gonna be talked about a lot in upcoming months, you've found yourself a market that you can sell your shovels to. Now, quick, find out what people may need and make it before someone else will and you got yourself a shovel.