As mentioned in this post, after Nimi, the king of his lineage came to be known as Janaka. The name of Sita's father was king Síradhwaja Janaka.
As per Mahabharata: Santi Parva, Yajnavalkya had discussion with king Daivarati Janaka.
As per above two names, it seems that Janaka with whom Yajnavalkya had discussion was not Sita's father. Also, in few places Yajnavalkya is mentioned as Krishna Dvaipāyana Vayasa's (who incarnated in 28th Dwapara after 24th Treta's Rama avatar as per Vayu Purana) disciple. But, many users on this site indicate that Yajnavalkya had discussion with the same Janaka who was Sita's father. Wikipedia also mentions the same.
Can someone please clarify if the Janaka with whom Yajnavalkya had discussion was Sita's father or some other Janaka?