Here is all of what Farage said according to Huffington,

When asked about Cox's comments during an interview on LBC this morning, Farage responded: "Yes well of course he would know more about extremists than me, Mr Cox.
"He backs organisations like Hope not Hate who masquerade as being lovely and peaceful but actually pursue violent and very undemocratic means.
"And I'm sorry Mr Cox but it is time people start taking responsibility for what happened. Mrs Merkel has directly caused a whole number of social and terrorist problems in Germany, it's about time we confronted that truth."
Forced to acknowledge that no-one has arguably been more on the receiving end of this sort of extremism than Cox, Farage said: "Yes and it's a terrible thing that happened to his family with the murder of his wife but he continues to be active in the political arena and as I say, given some of the organisations that he supports I can't just stand here and say 'I'm not going to respond'."