speaking of：speak of的现在分词形式，phr. 谈及；说到。放句首或句中都可。
speak highly of：赞扬；称赏；夸赞。

【例句】
Reading is the only hobby I can speak of.
读书是我唯一值得一提的爱好。

All who know him speak highly of him.
凡是认识他的人，没有不称赞他的。