Suitable reagents for nitration of thiophene
According to this reference by Katritzky et. al (2005) (see below):


  Thiophenes  are  easy  to  nitrate  compared  to  other  five  membered  heterocycles.  They  react  with  mild  nitrating  agents  such  as  copper  nitrate. 


The reference further reports the nitration of thiophene to 2-nitrothiophene by nitric acid/Trifluoroacetic anhydride in 78% yield.

The classic $\ce{c HNO3/c H2SO4}$ conditions are too strong and likely to result in substrate degradation.

Reference:

Alan R. Katritzky, Eric F. V. Scriven, Suman Majumder, Rena G. Akhmedova, Novruz G. Akhmedov, Anatoliy V. Vakulenko, "Direct nitration of five membered heterocycles," ARKIVOC 2005, (iii), 179-191 (https://doi.org/10.3998/ark.5550190.0006.320).