Find specific topics with topic modelling
You can use LDA (Latent Dirichlet Allocation), as input data it only needs different collections of text. As output it generates for each document the main topics (Like: Document1:0.3% Topic1, 0.2% Topic5, 0.2% Topic8, 0.2% Topic12, 0.1% Topic3) and for each Topic the different words with the amounts they contribute to that Topic. You can then browse the words of the Topics and manually decide how to name the label of each Topic.