I have checked Ragnar Lothbrok's genealogy to find if he had male line descendants to this day. It would not be surprising considering that he had eight sons and they became powerful rulers of their own. The main issue is that the genealogy is disputed. If enough Y-DNA lines survived, it would be possible to confirm the genealogy by triangulating the various Y-DNA haplotypes.

Don't be fooled by the series Vikings. Ragnar did not start life as a farmer whose fortune rose after he found a way to navigate to England. He was the son of (semi-legendary) King Sigurd Ring of Denmark and Sweden, himself said to be the son and grandson of other kings of Sweden or Denmark.

The most promising lead comes from the Uí Ímair dynasty, said to have been founded by Ivar the Boneless (Ragnar's 3rd or 4th son), although according to Geneanet's genealogy it was founded by Halfdan Ragnarsson (known as Hvitserk in the TV series), who were both at some point kings of Dublin. In any case, they had the same Y-DNA. One of this dynasty's cadet branches is Clann Somhairle (Clan Donald and Clan MacDougall), which have already been confirmed to belong to R1a-Z284>L448>YP280 (actually Somerled is said to correspond to YP326 further downstream, but YP280 was formed 1500 years ago and appears to be the marker that separates the Scandinavian branch from the British Isles, so most likely Ragnar Lothbrok's original lineage, if indeed it is his Y-DNA).

Clan MacLeod is said to have been founded by the younger son of Olaf the Black, King of the Isles, who belonged to the Crovan dynasty. This dynasty is also an offshoot of Uí Ímair and therefore should have the same Y-DNA. Surely enough the MacLeod Y-DNA Project has over 20 members belonging to R1a-Z284>L448, and some are confirmed for the YP280 subclade.

Other lines may not have known descendants to this day but remain historically important. Knowing Ragnar Lothbrok's Y-DNA would also include the following royal lines.

Ragnar's eldest son, Björn Ironside inherited the title of King of Sweden and his descendants kept that title until Emund the Old's death circa 1060.

Ragnar's second or third son Sigurd II "Snake-in-the-Eye", King of Denmark, who was supposedly the father of Harthacnut I of Denmark of the House of Knýtlinga. The most famous member of that house is King Cnut the Great of England, Denmark and Norway.