All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
If the oath is repeated on one same thing, such as saying “I swear by Allah, I will not talk to so and so”; and then he spoke to him, and he repeated that oath again, while he did not expiate for breaking the first oath, then he is only required to expiate once according to the view of the majority of the scholars.
However, if the oath is repeated on various things, like if you said “I swear by Allah, I will not talk to so and so”; and “I swear by Allah, I will not travel", then in this case, one must expiate for each oath according to the view of most scholars.
If you do not know the number of oaths you made, then you have to estimate their number, according to your predominant belief by which you think that you will be acquitted from sin. Therefore, if you do not know the number of oaths you broke, then you should endeavor to know their number and act according to your predominant belief, and then you expiate for them.
According to some scholars, it is only one expiation that is obligatory even if someone has sworn many oaths.
For more benefit, please refer to Fataawa 311782, 332521, 162559, 87181, 138168, 375016 and 189081.
Allah knows best.